The reason I have suggested using either the A12A or late A13 rods, or as an alternative, boring out late A12 rods is because these have more material at the little end. The factory made the rods that used the larger 19mm pin with more material for a reason I presume.

If you bore the earlier type of 1200/A12 rod, there will be less material around the pin to support it. Having said all that, I used bored out 1200 rods in my engine for many years without problems, but my engine never went over 5,500 rpm & was in a relatively modest state of tune.

So here's my recomendation. Try to find a late set of A12 rods, assuming that the A12 engine was used in the B310 models in South Africa. As I wrote, these seem to be the same forging as the rods with the bigger pins, but simply bored for the 17.5mm pins that the small bore engines used. Preferably the rods will be diamond bored to the finished size.

As for the compression ratio with the big bore, well I never had a problem & I installed a brand new 1200 GX head over a 76mm bore in my 1200 engine. Later on when the engine finally wore out, I bored to to the first oversize [76.5mm], overhauled the head, & stuck it back on. It ran on pump fuel & with the stock GX distributor, it never detonated as long as I used 'super' grade fuel [about 95 to 97 octane I think]

Too bloody easy mate.