The oil pan is pretty much the last thing that I want to leak on a BB A-body with headers and stock K-member so I use good crush-proof gaskets such as Superformance, gray RTV on each side of the gasket, I let it set up just enough that it doesn't squeeze out everywhere when installing it, lightly snug the bolts. Tighten the bolts the next day. If I'm in no hurry I give it as many days as possible to cure before adding oil since I normally do this kind of stuff during the winter.

It's not fun to remove the pan and clean but that's better than dealing with a leak.