A12A was a performance option of the A12: Larger bore, and was fitted to sedan/coupe while in the same market the A12 was fitted to wagon only. So all around a better engine than A12. About 5% better.

A12A came with:
* Different pistons & cylinder heads in different markets/years [edit:] all appear to be round port heads
* Dry manifold [edit:] Canada
* Wet manifold

A12A used the same Connecting Rods as A13 engine in B310. They feature the larger A14-size gudgeon pin, instead of the smaller pin of the earlier A12.