For availability check local junk yards, and ebay. As far as a rebuild goes, the heads will need to be: cleaned, dissambled, valves checked, valve job, resurfaced, assembled, springs checked and shimmed for correct spring spressure. You will have to buy aftermarket springs if you run an aftermarket cam with more duration/lift. Expect to pay about $250-350 for machine shop fees depending on what you get done and where you go. Springs are about $100-150 extra. Valves cost $10-15 each extra. I'd say 2.00 or 2.02 valve are the bigger valves you can fit on those without having to install larger seats. Installing larger valve guides is about $15-20 per valve. Installing larger valve seats for bigger valves is usually $15-20 per valve.