As mentioned in my other post I've been doing some research and today's find is that KLF300 pistons are the correct pin height if one wanted to do an A15 crank into an A12 block. No clue of the skirt will hit the crank but at $30 for a cast piston it could be worth investigating. They are flat tops with two small valve notches.

2009 Kawasaki KLF300 is a 4-wheeler with single-cylinder 290cc engine. It has a similar power-to-weight ratio as a 1200 (it's not a light motorcycle with massive HP more like 16hp/500lb and same compression ratio as an A15)

76cc pistons (same as A15)

A12 pistons are 67.4mm long, A15 is 65mm long

what is the KLF300 pin height?

26.5 ?

Not sure on pin diameter

The pin height is 26.50 so they are going to be .1mm short but I wouldn't think it enough to worry about. Near as I can tell the pin diameter is 18mm; so you'd need to either bush the A12A rods or bore the A12 rods.

Additionally KSF250 pistons(KLR250 might use the same one) are the same 26.50 pin height and come in 75mm (1mm oversize) so in theory you could bolt them into an A12A block (I happen to have one).