The comp gasket will add back closer to .020. So if there really is .045 off, .025 is left. Hoosier Hurricane suggested I mill the intake side of my 113s rather than the manifold. You would have the flange taken down .035 theoretically, 1.4 times the net loss from heads and deck. If there is a less than exact history on the heads I would cc them to give further evidence of the degree of milling. .045 removed should put the chamber size in the neighborhood of 65 cc I would think. Then go on the conservative side regarding flange milling and have .030 removed.Or you can do as Charlie suggests, and if they bolt up and hold seals, go for it.