How to figure out if oil pump is working?

Go through the best practices to make sure that things are loose and ready to go. When you drain the old oil, look for water and, yes, a gas smell. Add fresh oil; 30W non detergent.

Once you are ready to spin it, remove the plugs, get a good hot battery and spin the engine. You should see oil pressure on the gauge. It may be only just a little off the bottom peg, but if you see oil pressure at this point, the pump is probably OK and most oil galleries are open.

Go ahead and start it, but at first start, watch oil pressure very closely. It should come up quickly and there should be no funny noises. Resist the urge to run it up as fast as it will go. A little acceleration is good to get some oil splash on cylinder walls, but "tightening the bearings" acceleration isn't a good idea just yet.

Good luck. Let us know how it goes.