Doug,
To answer your original question... Yes it could very well be the oil pump.
Had an old Ford Y-Block a few years ago, that started doing the same. Put a mechanical gauge in, which confirmed the problem. Swapped out the oil pump and was good to go.
Got really lucky on that one, as the oil pump was an external version. Never even had to drop the pan.
I think you're plan to install mechanical gauges is probably a good one, as then you'll have a better idea as to what your oil pressure truly is, before you tear into something that may not need torn into.
Good Luck.
