Depends on what type six you have. Do you have one of the later chevy 6s (230/250/292)? If so, then FelPro 9786 (?) should work for you. It's a metal embossed gasket that inline racers apparently have used successfully. According to Leo Santucci's "Inline Power Manual", it holds up best for all applications.

If you have another series six then maybe someone else can offer up a good choice.

-ftyler