No Oil Pressure

I was given a low mileage, good running 225 out of a '64 Dodge pickup to replace the worn out 225 in my '66 Valiant. I was told the engine ran great.

While it was on the engine stand, my Dad and I turned it upside down so we could swap the oil pan out. The Valiant has the stock dummy light as well as a SW Oil Pressure gauge. Upon startup, the needle didn't move and the oil light stayed on. I started it a couple more times, but still no oil pressure building and no oil coming out the rocker assembly. Did I lose prime turning the engine upside down?

I ended up pulling the inspection cover on the oil pump, packing it full of Vaseline and putting it back together. Still no oil pressure building.

Any help would be greatly appreciated, I'm stumped. Thanks in advance!