I remember Robin Booth did this (and I'm pretty sure that is his moke Terry is refering to and he also know where it is
), however for a long time Robin swore black and blue that it was better than a 1275, until he did the Canning Stock Route and it was apparent there that the 1275 mokes were as good or better, especially when it came to fuel consumption. Robin did change his mind.
You'd also have trouble getting bits for the gearbox and possibly the engine.
IMO, there are much better converstions you could do these days, but whats wrong with the A Series Engine.