Before you do anything else with the heads, clean the head gasket and valve cover gasket mating surfaces of each one really well with a coarse rag and lacquer thinner and measure the head thickness (all 4 corners of each head). Take your measurement between the valve cover gasket flange and the bottom of the head with a good caliper and make sure it's squared up on the head. The standard spec is 3.310"..... any less and the head has already been resurfaced. Get a good measurement all around on both heads.

Next, turn the head upside down and put a straightedge (metal carpenter's 24x12" framing square is what I use) end-to-end down the middle of the head. Turn off any bench lighting and shine a flashlight toward you from behind the straitedge. If you see any light coming through at the bottom of the straightedge, that's the warp you'll need to deal with. Move the straightedge from side-to-side on the head, but parallel to the head C/L. Measure with feeler gauges to find the amount of bow. Then put the straightedge on both diagonal corners and get another view of it. Anything more than .002-.003" and you'll need to try to find someone to straighten them - or get another set of heads.

Frank