I had an AWD Evo-engined Colt in 'The Other System's First-Party Simulator', that thing was just the most insane thing I've ever virtually driven. Gear ratios shorter than Tom Cruise, rearward torque distribution, the biggest, softest tyres available... Yeah, it almost makes me want to play it again.
Engine swaps in GT5 would be a great addition, but I can't see it happening and I personally would only use it on cars with originally dull engines, I mean I'd never swap the engine out of an AE86 unless it was for the AE111's blacktop 20 valve 4A-GE, for instance. A 20B triple rotor in a 323F, however...