Dog
Thanks for your reply.

I thought that i was fairly familiar with the "A" series engine & as far as i knew, they used only 73 & 76mm bore sizes, but with a 75mm bore, you are right, it yields 1237cc. This is a size not sold in Australian models & if one were to bore for the 75mm piston, one might as well go on out a little more & use the 76mm piston from the A14. At least it is an available size for us.

As you pointed out, the boring out of the little end of the rod is a pain, but not a big one & any competent reconditioner should be able to do it. After all, it's only "a few dollars more"

Repco [REplacement Parts Co] is an Australian supplier & manufacturer of [surprise surprise] replacement parts. To cut costs, they cast one piston for the A12 & machined it with a dish for the 1200 models, & machined it flat for the A10. Same "replacement" piston, two compressions, but only in 73mm sizes.
Chris
PS With a 76.5mm bore [first oversize] & a 70mm stroke you get 1287cc, so thats still comfortably under 1300cc for competition use