If you were getting oil pressure, and then immediately after all the work, stopped getting oil pressure it's very doubtful you have worn out bearings.
Even with worn bearings you will still have some oil pressure.
Capt. Obvious says, "Did you forget to install the oil pump drive shaft?"
(one of the best mechanics I know has done this
As suggested above, put a mechanical gauge on it (temporarily under the hood) to know for sure what's going on.
And spinning the oil pump from the top side with a drill is a good suggestion also.
Something else to check:
Did you put the engine-to-body ground cable back on?
Are the other gauges working properly?
Let us know what you find out.