[mattybilt79]

If I'm reading this correctly you want to swap your 78 motor and front clip over to a 91 truck. By the time you pull your motor out and pull the bad motor out of the 91,swap all the accessories and TBI parts, exhaust and do pm stuff like timing chain and rear main since the motor is out. Then deal with the 20 plus year old wiring harness which will have brittle wires and at least a few broken connectors no matter how easy you are when disconnecting them. It could be done but you would have two non running trucks and a can of worms of other issues to deal with. The 91 should have a 4l80e like you stated overdrive which is a plus but from my research and personal experiences a total pain in the ass when they go bad. It would be a big job just to upgrade to power windows and locks. I would either rebuild the motor in the 91 or find a year compatible motor to put in it and then add your front clip when its running and driving or keep looking for a compatible pre 80 truck with the accessories you want that needs a motor to swap out your 78.