If the seller has done what he claims, and the hot idle oil pressure is showing "0", then it's time to temporarily install a mechanical guage on the engine, and get a reading on the REAL oil pressure.
If it's as low as the electric guage says it is, then the problem is probably loose bearing clearances, and, at a minimum, a new bearing set will be needed.
WANTED--MJ Comanche to restore. Must be solid, (relatively) rust free chassis. Send me a PM if you have a line on one that is for sale.