I think the breaking point on year models that can be converted easily is when you reach a point in the newer models where the transmission and things other than the engine/fuel/spark delivery are controlled by the vehicles computer. For example I have a 1989 Chevy P/U that's a stick shift and the only thing the computer controls is fuel/air/spark delivery which would make it easy to convert back to the old school carb, mechanical fuel pump and HIE distributor. In fact now that I no longer have to smog it...it just might end up going back that way when its time to rebuild the engine that has about 160K on it!