[swamp rat]

Absolutely a 4 bolt. Sludge is from running the oil too long (non frequent changes) and thermal breakdown

>>> Also, there was no sign of a gasket/seal under the head covers or intake manifold, is that normal???<<<

Its common to not use the front and rear intake manifold gaskets and replace with a 1/4" bead of proper silicone, it is not normal to omit the intake to head gaskets, these gaskets seal the intake runners as well as water ports.

I'm gonna predict your bearings and other ware parts will show some abnormal wear, push rods, rockers. hopefully the crankshaft will still be a good serviceable core, plan on replacing the camshaft and lifters, which is normal.

Per the heads and block, unless they find any cracks then they most likely are fine.