well ive had it on a steel gurder as a straight edge, with a 1mm raiser on the straight edge and heated it and clamped it down, i started with a 3mm raise at each end, it now has a 1mm raise at each end with a 0.5mm kink where the bend was but the kink is inbetween ports anyways so irrelevant, im sure the manifold will pull in 1mm, and i have a stock nissan gasket which is 1.3mm thick and plyable so it will give more than a multi layer steel.
im going to take it to the welder in the morning and see what he thinks, im sure it will go now though