My 77 F250 has a 400 in it right now with the NP435 4spd. I'm going to be installing a 460 within the next few weeks but I am unsure what to do about the flywheel. The 460 has a flexplate due to it being mated with a C6. Can I reuse the flywheel from the 400 or do I have to buy a new one for the 460? If I have to buy a new one can I buy just any 460 flywheel or is there a certain one I need due to balancing issues? Thanks in advance for the help!

 

The 400 flywheel won't work. If there is a counter weight on the 460 flex plate you will need a counter weighted flywheel.

 

A 390 flywheel will work also. Is there a reason you are not using the 4 speed?

 

Depending on the year of the 460 it may be internally balanced and it could be externally balanced.
Before you stick just anything on it (like the 390 flywheel) make sure you know what you have. Look at the flexplate that was removed and identify the counterweight on the harmonic balancer.