do the heads on 1960s beetles have hardened valve seats standard?

Sure do

one of my heads has a crack between the valve seats. is this a real problem being air cooled?

cheaper to buy a new or secondhand head compared to getting the cracked one welded as you gotta remove the valve seats, chase the crack to the bottom of it, fill weld the crack in and then machine for new valve inserts.

Repairing the crack depends on the crack and the type of rebuild/repair your're trying to achieve

Well I was going for the permanent solution cos to TIG the crack up you should really chase the crack all the way out so that when you weld the weld isn't contaminated by carbon n oil that will have seeped into the crack.