Sheet metal gaskets have been around for ages. I've seen them used both in OEM and repair assemblies. It is true that they are a little more reliable when used on freshly machined surfaces, but I seldom had trouble when using them in other situations. In fact, I had one of the old Chevy 409/425 engines that came with two head gaskets installed by the factory under each head to lower compression. I removed the heads and discarded one gasket from each side and reinstalled the heads on the used single gaskets. The engine ran for several years without problems.
As to the use of gasket compounds, I always used K&W Copper Coat or spray High Tac. Never heard of any aluminum or other "powder" being used. seems to me that any granular foreign material would likely defeat the purpose of a clean surface and the gasket.
I HAVE seen silver or gold metallic paint used as a gasket compound in a pinch.
