I was driving home and had pulled up in front of my house (at idle) and heard "rattle, rattle" (440 engine) & saw my oil pressure had dropped to zero, so I shut the motor off. Thank God I was in front of my house. It sounded like the valve gear rattling & not the deep "clunk, clunk" of a rod/main bearing (I'm hoping anyway). The engine did not seem to have any type of misfire.

These are the things that I can think of that could cause this problem.
1. spun main bearing
2. spun rod bearing
3. spun cam bearing (#4, right?)
4. leaking line going to the oil pressure gage
5. oil pump failure
6. REALLY low oil (was 1-1/2 qts. low per aftermarket dipstick). I don't think the pickup sucks air until about 3 qts. low (?)
7. Oil pump failure
8. sheared off the hex end of the oil pump/distributor gear

I'm afraid to even crank the motor until I find the problem. Obviously I don't want to pull the engine if I don't have to.

How do you guys suggest I go about fixing this problem? What order should I check everything? Can I see the hex end of the distributor/oil pump drive if I just pull the pump off? How can I tell if the pump went bad?

Any help is appreciated. Thanks in advance.