I am swapping out my flat tops for a fresh set of round tops from ztheapy. Which PCV tube will I need? The 70 or 71-72 or something different? What's the difference?

You might want to try searching this forum:

http://www.classiczcars.com/forums/forumdisplay.php?f=61

I just searched, and there's a few threads on flat-round top swaps -- but no mention of PCV tube. Sorry I can't help you.

Are you talking about the hose from the block to the balance tube, or the hose from the valve cover to air cleaner?

I kept the original hose for the block to balance tube connection. The person I bought the air cleaner from on ebay threw in his old hose for the valve cover to air cleaner. It looks like nothing more than 1/2" oil resistant hose (maybe a slightly larger size ID, I've never measured)