You don't need to torque the heads to spec, just to about 45 ft. lbs. Modeling clay is what most people use. Get it from an arts and crafts store. Be sure to smear some motor oil or grease on the pistons and valve heads to keep the clay from sticking to them. Rotate the engine through a couple of complete revolutions by hand to compress the clay, then remove the head and measure the thickness witha a machinist's ruler. Check the pistons in several different areas, the domes and and around the edges. .050" to .100" over the pistons is good, but performance suffers a bit with piston to head clearnce over .050". Valve clearance shoud be at least .040" with a a gasket thickness of .55", a bit more is better for flow. You can reuse the gaskets.