Since you already met with Bram, you must have spoken to him about building a model like this.
It might be easier to convert a Roundhouse model, like Riverdale do - they are based in Son, not far from Eindhoven.
This is from their website -
Riverdale Locomotives is specialized in G/16mm scale coal-fired locomotives.
Our newest coal-fired locomotive is the Darjeeling 'B'. More details on the DARJEELING page.
New is the steam pressure telemetry feedback with automated damper. Details here.
The coal-fired locomotives can also be home built with our coal-fired boiler kits in combination with proven Roundhouse kits and parts. Alternatively you can convert your existing gas-fired Roundhouse Lady Anne, Billy or Katie into a coal-fired Amy, Elke or Irene.
For a coal-fired locomotive in particular, building yourself saves your “railway company” a lot of money and the process itself is very rewarding. Our kits are designed in such a way that only simple tools are needed. Check what skills are required on our Frequently Asked Questions page.
Don't think our coal-fired locomotives are difficult to drive. We're using a special boiler design with a coal-fire damper on the firebox door. Our locomotives can be fully remote controlled should you want it. And you find detailed operating instructions in the extensive manual which comes with your locomotive/kit.
To assure quality and reliability we're using modern design and production tools, such as Computer Aided Design (CAD), computer based calculation programs (FEM), computer based production (CNC, laser cutting). We have all the skills and experience needed to assure the quality of our products. And we deliver all service and support you'll need for your locomotive.
You can contact us by e-mail : email@example.com or by telephone: +31 499 476808. You find us in Son, a small village nearby Eindhoven in the Netherlands.
@ tac, Thank you very much for the detailed info. To speak frankly i have to share some points/thoughts(to all i guess). The conversation i had was about the bigger locomotives he had or could order, but he is not the only one, sorry. The locomotives i would like to have are at the most diy assemblies/kits. Those ready to roll big ones are far out of reach of my wallet or they donot exist! If i have to pay a mire 15000 euro for a big boy on coal in 1 at 32 scale.....with my tool shed, knowledge, experience and with some help to fine tune i think i can build several of them. This is NO insult to U.
@ To all:
As we say in the Netherlands: i did not fall on the back of my head(oke that was freely translated from: ik ben niet op mijn achterhoofd gevallen(_ The other problem is also: i would like to build the bigger ones that are on my wish list, if i order those.....even as a kit......sheeeeeeeeeit! My wish list is....well......big...........oke here it is.... Challenger Big boy aa20 Hugh boy Big Joe eerie 9999 some garats My grandfathers loco, NS6300(For sure) And our Dutch pride: Bello (a t3 if remember correct, Just for the sports)
To make cylinders, i suspect some tricks and difficulties. They are not really difficult to make, i suspect. I saw some drawings and makings(most vids on yt and old school books), it is not that hard. A cattle to boil water, i already bought some copper pipe. I think this is the most easy part. If i know how it works (incl drawings) i can build it. If i have drawings(incl measurements) i can make it true to scale.
Funny: tomorrow it was 3 years ago sinds my old man past away.......we sold every thing to make this stuff(was his).....a 35 year old wish, a big boy coal fired on steam.....funny how life takes his turns I will be needing a new lathe and all other articles....
But those other things i am not aware of.... I can make a sand cast to cast the wheels in aluminium/brass ect Over pressure valve. I am seriously thinking (i know) that i am capably of doing it. For the forward and reverse and speeding i still must figured out, but i have a idea(simple mechanics....) BUT there is more: tricks than my eye will or can see, building is one, make it work all together is two.... To avoid mistakes or create a spaghetti monster: that kind of knowledge i dont have, and that kind of fine tuning knowledge you can only find in books and forums.... Forums give you a short cut how to reach something, and are a BIG HELP........But i would like to know the whole story incl how and why! Incl power calculations ect.... It will take time and a learning curve, first lets built a boiling cattle that operates on coal and can drive, just to get my toes wet, does not even have to be a loco....just a pipe that can huf and puf around my tracks....and haul some things/grams/grains...
The forums provided i will surly take a dive. There are two book hints and forum hints on this topic, perfect, if there are more hints, tips tricks books vids.....what ever YOU think i miss or you think i must read or watch or learn......please...i really would like to know about.
Thanks for reading and all the tips/comments/warnings/ect you can provide, and understanding of what i would like to achieve......in the long term! Thanks and with best regards, Igor K
Igor, in that case, the very best advice I can give you is to join a 5"/7.25" gauge model engineer group like the one that my friend Remco attends, although in his case, it is just for Gauge 1. The experience of the builders that you will find there will give you a better idea about what is involved in building a large coal-fired locomotive of any kind, let alone an Erie Triplex 
I have to say that your plans are very ambitious and will all be VERY costly to achieve, as well as taking a long time, and requiring a huge amount of experience.
I've just been talking to Remco Vegting, and I've sent you his email address in a PM.
To be honest, I can't think of anything more to tell you, so good luck and tot ziens.
Thanks you for the kind words and encouragement. I sure will keep you updated. From all the bits and pieces i gathered (not much) i think it will be wise to buy first a complete kit.
Basically after that, it is copying the "steam system" like billy1906 does at: my large scale forum...one loco after the other~~ There will be some obsticals...try and error and succeed.( i really must learn myself to post also success story's and not only mistakes and questions! Rattle my chain ones in a while if it happens again)
Speaking frankly: after "discovering" the right terms, tools, part shops and the proper vids on yt it is not even difficult when you get the whole picture complete. You dont need so much machinery(from my point of view) a decent lathe, a cutter with x-y table, saw table with proper blades and a standing drill are a must. Your own melting/casting/forging stuff with sand castings will also be very handy( up to 1800 Celcius btw for cast iron. Copper, 1200 will do the trick, brass and such 1000 ect)but not a must. MIG welding with optional torch or a good torch. a 3d printer. A uncle that owns a scrap yard is also very handy I think i will manage