1966 273 v8 cam suggestions and exhaust too?...it will never be super performance but

Well, a lot depends on what you want to do with it. In example, is there a time you want to run in the 1/4 mile? The little engines need a bit of gear and rpm to run hard.
Also, on exhaust sound, I would certainly suggest going to a few car shows/meets and listen to what's out there. Once you find a sound you like, go on over to the car owner and simply ask. Car owners love questions about there car and even more so when you compliment there cars sound. Ask'em what he runs and they'll just spill there guts.

For your 273, the hard part about the rebuild is pistons. Egge machine makes slugs for your mill. Other than them, I do not know where to look. I'm sure another 273 owner will pop up and help out with the slugs.