I haven't found an engine production information source.

Some info could held narrow it down to the B20B, B20E, or B20F category.

1) Does it have injector ports? I.e. a bolt hold and (covered somehow with carbs) hole on the head between the valve cover and each intake port? If not either some rare late model marine motor (unlikely) or (likely) a B20B.

2) If it does have injector holes look at the metal surrounding the cylinder head bolts in the middle of the head along where the intake and exhaust manifolds bolt on. If the flat surface the bolt connects to is sort of an island, its a B20E head. If it has a small flat machined surface that connects with the injector mount surface then its a B20F.

3) If it's a B20F there is no way to tell if it's early (6 bolt) or late (8 bolt) without looking at the flywheel.

All the above to the best of my knowledge.

Why do you need to know? The engines are all nearly identical - at least as near as normally matters unless being rebuilt.