Further to all of this Mark came round to see me with his Loco and MTS Gear today. Bit of a brain bender this setup. I quickly discovered that the Loco was not Chipped as Mark had thought. But did run happily on my Massoth System as an Analogue Loco on address 0 Motor Whistling as expected and the Sound Very Loud. Sound was reduced with the Volume Adjustment on the B Unit. Here is where things get a bit tricky, on Marks MTS the Loco would not work on 0. So I got one of my Locomotives (Loco No 16) out which ran happily using Marks System. Hm....
So we went to my Workbench and I pulled the Loco apart in an attempt to see if I could Chip it up. It has the Direct Decoder Sticker but needs the Chip to be wired in. I only had 1 Chip so that was no good as it needs 2 55021. So looked at GRS Site they have a 55021 but listed as a III. Will these be compatible to Mark’s System which I think is a bit of a mush mash between Serial and P?
As you can see the Left Hand 55016 has P Sticker on the rear but is just 55016. Whereas the 55016 on the Right has 55015P ref no on the face. Not encountered this before but I guess that means that both Handsets are P? However his Central Station does not have a P so I am assuming it to be an old Serial one.

Finally a look inside the Loco. It is not a Plug In Type as expected with this below

But the Circuit Board has the possibility to Wire in 2 Decoders via the Pins as seen below towards the Top Right of the Board. The 2 missing / empty Sockets are where the Lights to the Front if the Loco Plugged in and the connections for the B Unit. I unplugged these to see my way round on the Board.

So to summarise the Help that Mark needs.
Does anyone have a 55021 Chip (not III) that Mark can buy?