G'day Amshaw

if your mate's V8 had ignition problems (leads breaking down) there is a possibility that it has cross-fired at revs, that has a habit of snapping crankshafts that would give the oil pressure loss, as said by others a good S/hand V8 should be easy to find and just replace it, don't forget that early 3 door Discos will become collectors items in the not to distant future like early Rangie 2 doors are now

cheers