Nice work mate, thats how I started too, an RM 100T with a 125 barrel plonked on top. Nothing was done to alter the stroke which remained at 50mm instead of 54mm, but it actually ran, albeit with not much power. I now have a 125 crank to yield the full 125cc capacity. Correct me if I am wrong, but I think you have the exhaust and muffler mounts in the wrong positions, ie; the rear mount (steel) at the front and the front (aluminium) mount at the rear, this might lead to the exhaust burning through the top of the air box if there is bad positioning or insufficient clearance? I also make it as a a 1980 "T" model, given that the chain is running on a solid nylon buffer, rather than the roller mounted atop the swing arm as the 1979 "N" model does. I have also upgraded the suspension to 125 specs, as in 38mm forks and triples to match and aluminium swing arm with reservior shocks. All said, there is great parts interchangeability between the 125 and it's little brother. I reckon these bikes are a trip to hoon around on, do you race yours?