Similar in some ways yes, but you must have a full interior (you can get away with sound deadening mind), the engine can be modified, as long as the inlet stays stock (that includes throttle body and injectors), but headwork, cams, bottom end work, dry sumping aftermarket ECUs, higher compression pistons etc is all permitted. Long storke cranks are permitted, but you wont be able to enter some championships (the welsh one for example) with them, although you will be able to enter the rallies. Transmission wise straight cut and bog boxes are allowed, but no sequential shift (not any more, you were allowed 5 or so years ago), suspension is fairly free, as are breaks, just no carbon ceramics, bonnet and bootlids are fine, as are windows (but leave the stock ones in, its a pain for marshals to sign time cards with those little slider things! The car must be one colour but stripes where fitted from the factory are ok (fiesta ST, escort mk1 RS2000 etc), no big arches and only 4 forward facing beams (so stock lights plus one pair of spots, apart from the some of the Midlands which don't allow spots at all). Wheels are fine provided they fit in the standard arches, tyres in Wales must be E marked but elsewhere you don't need to worry. Hope that clears things up a little.