Q&A for a`65GT
For front disc's you can go to SSBC kit A153, you will need 10" drum spindles for this kit and keep your SBP ralleys. With the 10.5 bell housing I had to fold over the firewall to floor lip as it rubbed there. I would order the big block A body torsion bars for good handling, and I would think the 323 gears should be ok, but I don't remember what my Car rpm was a 65 mph, I thnk it was slightly higher but I had low tires on it back then.
I'm not sure about your Z bar as I never did an earliy A body V8 swap to stick car before, but I bet someone on here has.