Building a 350 will cost you more than any other motor (Other than an OHC) to get "fun" power out of. A mildly built 455 will cost less and be loads more fun to drive.

However, to answer your question, I'd recommend any of the 72 cc heads from 1967 to 1970. Then have them decked slightly to get to a real reading of 70 to 72. Most are bigger, ranging from 75 (#62) to 80 (#13).

For the cam, any of the 068 "Copy Cams" are good, like the K2801 from Summit. This cam will "feel" a lot bigger in a 350 than it would in a 400 or 455. Also go with the factory 4-Bbl or a Performer, but not the performer RPM. The 350 is a little to small to flow the RPM on the street.