If it is all apart I highly recommend MLS gaskets. Have ZERO leaks since switching to MLS and a light spray of copper coat even though they say not to. You would have to have the cylinders and head surfaced to mls spec. Should have them machined anyway as they are almost always not 100% flat. If you are not going to have them machined then get a Cometic soft graphite head gasket. I get mine from Dynoman. Dont use the cheap 836 head gasket from Cycle X they will leak oil, they are too hard and dont conform to the surfaces. I use nothing but Cometic head gaskets anymore, they dont leak but they cost a bit more. Have had bad luck with other brands and a head gasket is no place to be cheap unless you like pulling cylinder heads. Remember must use heavy duty cylinder studs and use new timing tensioner rollers and cam chain. If you want a quiet motor need new primary chains too! Stock connecting rods? At a minimum I shot peen them and would highly suggest new bolts. Better yet Cycle X Super Rods! I know a person has to draw the line somewhere on these builds but I can suggest nice to have parts and must have parts. Let me know.
What brand pistons? Any idea? Might be hard to find new rings for them, may have to special order. The old 836 size pistons, different manufacturers use different size rings, yeah that makes it fun if they are vintage pistons.