You might want to do a search of the forum and read what the experts here have said about running a newly rebuilt engine on a test stand. Good luck and have fun.
Hopefully link works. Has been discussed in the past. Use the “search”. Mike
https://www.kaiserwillys.com/oil-pressure-switch-50-pound-engine-unit-fits-48-55-truck-station-wagon-jeepster
Assembly lube dried up and blocking oil passages? Plug behind cam shaft gear missing? Crank clean out plugs missing? Sounds like you might have to tear it down and clean it. Mike