I have sucessfully straightened aluminum heads myself. I talked my old machinist into trying it on a 2.6 head. I got him to clamp it to a steel plate, drilled for the inner head bolt holes, and shimmed the outer ends (the center of the head was bowed up) at about 140% of the warpage in the middle. IIRC, it was out about .010 at the center, and we used .014" of shims at each end, and torqued the center bolts to 80ftlbs at the center holes, and 50ftlbs at the next outer pairs. We put the whole assembly in his decoking oven and heated it to about 550*F for 12 hours. It came out with only a .001 warp, which we cut off. Cam bore came out under .001 of offness, which we align honed out. This head is still on my turbo 2.6 and I got at least 50k out of it before the stock piston broke under 21psi of boost (I got a little carried away with a boost increase using the grainger valve and had eliminated the 2bar fuel cut).