Assume there's very little warp in the barrels, the head is usually what warps and not much at that... remove the minimum needed to get them flat, no more. Ask to be told how much was cut from both. It's likely to be only a few thousandths of an inch. That won't affect the seal bores. Head gasket - original was pretty thin, and all current head gaskets are thicker. May be asbestos or other HS related? That can cause leaking at the oil feed holes as the seals assume the thinner original gasket. I do not have a solution for that yet. With a typical head desking to remove warp, head gasket thickness doesn't matter.
If you're decking to increase compression ratio this is a totally different matter. The problem is valve clearance, and increasing head or base gasket thickness to get more clearance just cancels the gain from decking.
