RMC's from the 90's are frequently classified as 'Single rail' or 'Double rail' and this relates to the outboard steel tube that formes the chassis i.e. is there a second outboard row of steel.
RMC went to Double rail to meet the standardized bendy test coz the single rail was not stiff enough
(you can weld in more steel but will have to cut up the tub to lower the body on if that is a single rail)
I have and old single rail and enjoy it a lot - but the quality of the cars that came from 'kits' of this era are more dependant on the build than the starting point (RMC is a good start tho)
Good luck
LoBelly
edit
this is Baz's twin rail RMC - judging by the footwell photo above I'd say the car you were looking at is the earlier single rail model
