Blown Head Gasket (advise?)

[Blue Collar Welder]

Good evening. I need some guidance on a blown head gasket. I am intending on taking my truck down to the local jr.college and have the students replace the head gaskets and basic carb tune. I blew the gasket out on the freeway under load w/trailer. I knew something was wrong as the engine was limping along. Ran a bit hot but I did not roast it.
My question lies in the amount of gaskets. What is sealing the distributer?
The truck stands with "82 Silverado longbed. Red over butterscotch, 15" Corvette chrome ralley rims. Kumo tires. The engine is a mystery. The cat I bought the truck from pulled the 305 replacing with a "mid 90's" 350 from a 3/4 ton truck. He pulled the fuel rails, put a cam in, air gap intake, chrome 1406 carb. Exhaust runs stock manifold through series 40 mufflers and dump close behind the rear tire. This truck runs stupid strong when well. I need to know what I'm libel to buy prior o getting there. Thank you - David