>>>*Did you by chance remove to oil galley plugs during the cleaning process?

If so, the one down by the pan rail gets missed quite often, it could be as simple as that plug not reinstalled.

But I have also seen these engines refuse to pick up oil pressure, I had one I started and read zero, I knew it had been built with lubriplate so I took her to 4000 and still nothing.

So we pulled the relief valve, squirted in gear oil, put it back and instant pressure.

Of course I also worked on one for 2 hours trying to figure it out, then I noticed the little wire to the sender was off...(Felt a tad dumb on that one...*LOL**)...*EB