David, do you have the knowledge, facility and tools to build a motor for yourself? If you do, great. But if not, you'll be much better off purchasing a crate motor or having someone build a motor for you. How much money do you have to spend?

The suggestions seen on here already about using a big block are valid. The '65 is quite a barge and it will take some cubic inches to haul it around in a spirited fashion.

Is the car running now?