Are you asking about the simply the cast block itself, or how they completed?
A short block is the block with crankshaft, connecting rods, and pistons installed. Basically, everything below the head gasket.
A long block has the cams and valve train installed.
A "6 bolt" or "7 bolt" generally refers to the number of bolts that fix the flywheel to the crank. There are other differences, a 6 bolt has larger connecting rods, and larger intake ports in the head...
The 6 bolt has 3 main caps for the crank, the 7 has a girdle. I have no idea if these are interchangeable. The oil squirters have different pick ups. the 7 bolt has different diameter head bolts.
Early 7 bolts have the notorious crankwalk issue, but I don't know if that is a block issue or thrust bearing?
