Yes the Ocra's are great kits, but well, they are a very long project. I have had a London Tram on the bench for getting on 3 years now. My problem is I am converting it to a Bogie Trailer for my Bury Steam Tram. Lots of mods to do, the Bogie was the easy bit. The upstairs will involve lots of new fabrication for the sides and roof. But before that I need to get the Stair Sides sorted a real pain in the butt. I have seen a different set of stairs in a book and may modify after building the individual stairs.
These kits are a Big job, but as Max says the end results are great.
JonD
) If I have a gripe it is that the castings are a little crude and he rolled up wire you can throw away to sub with some decent straight stuff. That and there is a little too much reliance on having to fabricate things out of wood. But then so did the original 
.....I too, have found that walking away from something for awhile results in a better finished product.