I just completed my 65 A/C rebuild and cured the belt squeal problem. I got a deeper and slightly larger diameter alt pulley off Ebay. I also read the manual regarding belt adjustment. Said to start with alt on full loose. Tighten belt with P/S pump. When done, apply any extra tightening with the alt adjustment. Seems to have worked as mine used to squeal terribly.
https://goo.gl/photos/CFWjgDUhQ2ZrW7tu8