Julian, I stand corrected on that one, never having seen or heard of a thick flange A7 barrel. At least it was a competition or export rather than home market product. Or do such things appear regularly and my assumption is incorrect?
The parts list you posted is interesting. On the basis that those are the only parts used, it does not make sense to me unless I am missing the point. As far as I know, the A7 crank only came as a small journal. The A65 rods 68-53 are big journal so can only be used with the 650 later big journal crank, which has an 84mm stroke. So retaining the original stroke and boring the A7 barrel to 70mm takes you back to where you started, and the barrel is too short. If I am wrong and the A7 crank was available with big journals, then it makes more sense...70mm bore, 72.6 mm stroke, A65 rods. The parts list indicates the original pistons and crank are used, so there is something amiss or I have missed a basic glaringly obvious fact. The length of the rods need to be long enough to allow the piston skirt to clear the flywheel at BDC.
No doubt the trick engine folks will put me right. Meanwhile I will check the parachute, anticipating the expected crossfire.
Regards
Swarfy.