no oil pressure

I built the 340 for my Duster by the book, got the special tool to prime the oil pump before i installed the engine, rotated it with a drill and got oil out of the sender hole in the block like expected. Six months later I put the engine in, crank over the engine with the starter about a dozen time and get no oil coming up to the sending unit ( I installed a tube/guage since I don't trust idiot lights). A new pump was put in during engine rebuild. I can't figure out why I don't have oil pressure. Could it be any of the following, or does anyone else have ideas?
1. could the pump have lost prime sitting over that long a period and I just need to crank it longer?
2. The engine has a 90 degree oil filter adapter for fit around the headers, is there some trick/angle to putting this on to line-up for oil flow?
3.Is it possible that the intermediate gear (oil pump drive) some how is not engaging the oil pump.