My Slant seems a little ill

A number of things can cause over-heating. At least on your car, boil-over usually causes no lasting damage, unlike most 82+ engines w/ aluminum heads that easily warp. First suspicion would be a water leak. My sister's 65 Mustang 6 cyl kept boiling over every 50 miles on a drive from FL to VA long ago. She stopped at one shop that said "must be the head gasket". I was only 16 then but knew enough to talk her out of that big expense and delay. Re-filled water, drove on and stopped at a busy shop that fixed it in 5 min for $5 - a pin-hole leak in a heater hose that you didn't see until pressure built up, and such a fine stream it didn't leave visible water.

If you had a bad head gasket, you would see foamy brown oil mousse in the radiator, like I did in my 82 Aries. Even with that, I could drive 25 miles home before it boiled over, which I did for a month before junking it.

If none of above, suspect lean idle. I had that for decades in my 69 Dart w/ Holley 1920, though it rarely boiled over. My 4th carb fixed that. My 65 Newport would also boil over, especially when my Holley Pro-jection EFI box got hot and made it idle really poor.