re. cam. How many miles are on it? A new cam and lifters will run you approx. $200 plus shipping.
Just remember new cam = new lifters too.
Measure and inspect the cam bearings too.... They aren't that expensive but are a pain to get to once the engine is assembled.....
re. machine shop. These old engines can build up all kinds of grit, grime and crud both internally and externally, a good block cleaning/dip is highly recommended.
If the block has never been bored, odds are it'll need it. Measure twice and cut once.....
Odds are even higher that the head will need attention. I've only worked on two Stovebolt 6's and both required new exhaust valves & seats. If you replace the valves might as well replace the guides too....
re. gasket kit. I've used 2 different master rebuild gasket kits, Fell-Pro and Best Gasket. I like Best Gasket much better and they are priced just about the same.
Good luck
Dave