1966 Pontiac 421 engine and transmission
Trying to figure out if I need to rebuild
it. Or try to sale it like it is.
See what other Grand Prix are going for in similar condition as yours. Usually you can't pull money back out of a vehicle. If the rest of the vehicle is in pristine condition it might be worth it to spend the money. But in most cases it's not. Especially if you've lost interest in the vehicle. Hope that helps! Jim
Unless your doing the restoration yourself and not paying others labor costs, JS is right, you will never recoup the money.
A 421 with the original trans attached is a desired power plant for several body styles in the early 60's. I believe that 66 was the last year they sere offered before dropping it as an available engine. Is it a tri-power engine? Is the trans a 4 speed manual? They are sought after combinations. If you do not want to refurb it yourself, it should bring a fairly good price by itself but if the car is in restorable condition and its the original engine/drive train, I would think selling it as is would be your best solution.