I have NOT done this, but after pondering all the stuff that goes into a car and where it all is, I'd make darn sure everything fits at the firewall. You have the engine/trans, steering column, brakes and exhaust all trying to fit there. The grille/radiator can move up/down some, and the back has only the suspension, exhaust and fuel tank fighting for room. Of course, you want the wheels centered in the body, but the firewall sets up just about everything else....