One piece rear main seals came in around '85-'87 (X or MarkZE will know).
Jack, I meant both Australian variants interchanged cranks/pistons/rods etc. Up to the point of metric flywheel bolts, anyhow. There is some difference with the thrust bearing - one is a half circle and the other a full thrust from memory - but not sure if that's a fatal discrepancy.
Evan, your motor from what I observed, had been "puttered" about. It showed no signs of having been beaten on long-term, or any old redneck fixes. Think it only had a re-ring. Pull the head and slather the bores in grease, anyhow. Then just tack it back together for the time being.