Rebuilt 302 casting heads available through Rockauto

I'd say give them a good look-over, clean them up and mask and paint them. If you cc the chambers, that will be good information for your engine build. If you want to see the valves and seats or the tightness of the valve stems in the guides, then you'll have to take them apart. Consult your mechanic.
When you remove your old heads, take photos of the piston at TDC and measure the distance it is down from the top of the block. Note if there any valve reliefs cut in the piston. If you have already chosen new pistons, etc., then, either way, you'll be able to calculate compression and select a cam to suit your needs.
At least that's what I plan on doing.
Did Rock Auto say how many are available now?