Found this 383, worth it for my 65?

Lots of opinions. An early A with a big block could be fun. However, in my humble opinion, you would be better off with a stout small block for several reasons.
1. 400 HP from a small block is easy without stroking.
2. A big block will be more difficult to install and run headers / exhaust. How much more difficult will depend on your skills.
3. A big block will weigh more. You can use a lot of aluminum parts to get the weight down, but it will still be heavier than a small block with similar aluminum parts.
4. A small block may not have the "Bam, in your face" visual effect that a big block has, but a small block can be dressed up nicely.