Look at the block at the rear under the exhaust manifold where the petcock for draining the coolant is. If it screws into flat surface or a shallow recess, it's a '69-'73 block. If it screws into a deep recess (maybe 1" or so deep), it's a '74-'75 block (different crank, rods, pistons, flywheel). There may be exceptions, but that's a handy rule of thumb.

If the head has no injector ports and no fittings bolted on immediately forward of the exhaust manifold, it's a carbureted head, the B head. If there are two holes there into the coolant passage, one large, one small, it's an EFI head (B20E or F). If it's one of those, look at the center head bolt on the manifold side. If it's alone on a round flat in the casting, it's a high-compression E head. If the flat is bridged to the bolt forward of that, it's a low-compression F head.

If there is only one place for a fitting into the water passage, it's a F head fitted for CIS injection. With carbs, this is functionally identical to the EFI F head.

If the bridge between the bolts is present but there are no holes into the coolant, it's a carburetor F head, never sold in the U.S. but not rare in other markets. Again, functionally identical to the other F heads. If no bridge, it's a B head with medium compression. The intake valves are slightly larger on the E and F heads than on the B.

I know of no way to tell which cam is in the motor other than removing the timing cover and having a look. Some are stamped with a letter right on the front, some you have to take the cam out and look on the rear. If it's not a Volvo OE cam, no telling where it's marked.

Don't worry about which distributor is "correct." The two good ones are the -007 (last digits of the part number stamped on the side of the body), which has centrifugal advance only, and the -085, which adds vacuum advance -- same performance, but better economy. Another common one has vacuum retard (can't remember the number), which is best just left disconnected.

I must point out again that there are very likely exceptions to all this, but that's what I'd look for...