340 tune up

that ain't no tune up, that's a top end rebuild!

i'd run a compression test and a leak down to get a baseline and then do an overall assessment of what you've got going on before jumping in deep.

Yep. Do this and go from there.

My 66 barracuda still has the original radiator. A lot depends on how well it was maintained.

Welcome to FABO. Have fun with your car as you get into it.