This is more or less what I'm facing right now. I'm stripping a motor from what I was told was an A7 (and the number stamped on the case certainly confirms that AA7 2953) of about circa 1950.... but....
According to the trusty '49-'53 spares manual numbers stamped on the components seem to bare no resemblance (living or dead) to the manual. But I digress.
What I have found is... a cylinder head number 67-381 (not in aforementioned manual), a barrell (sleaved) numbered 67-253[ A10 of vintage definately), conrods 67-391 (vintage?) and polson pistons 385.
The barrell and pistons match (sort of) in terms of bore - pistons measuring at 2.610" which I think is within original A7 spec, and infact they are an australian manufacture.
What may be important to the original question though was the massive build up of carbon on top of the pistons and within the squish area of the head. Depths went from about 3mm to 5mm across both surfaces. There is also discolouration in both the barrells and crankcases which may indicate pretty significant heat, but if this is related I don't know.
Ulimately I hope the experts here may have answers for us both, but whoever built this motor before I got it, I suspect enjoyed it for only a short period of time.