Weight wise the rs1800 is slightly heaver but only by a few kg..

the rs1800 shell has some revisions to it over a mk3 rs turbo this is why it is also known as the mk3.5...

the doors have impact bars welded in and the dash area/steering column has braces which can be removed with a socket set..

I converted my rs1800 to rs turbo and with the aid of loosing metal, poly windows and few other parts, got the overall weight to 820kg with a weld in cage.

Im now going back to zetec 16v engine which im turboing...

as for a standard rs1800 they are 132bhp i believe not sure on torque figures.
with cam chip exhaust etc i would imagine 150 was possible and a higher rev limit then if you go throttle bodies bit of porting and good managment 200+ would be achievable and with a real strong engine.