Much as it's never been in style to say anything nice about Indy, Diamond makes a stocking/shelf piston for them that looks pretty nice with a 7.100 rod. It does use support rails for the oil ring pack.

It uses a 990 pin, has 1.35 compression height, weighs 695 grams and uses standard 1/16-1/16-3/16 rings. There aren't any tricks in them, just a relatively short compression height. Has a 73.9 cc dome per specs, I have not CC'd yet. 804IN is the package number.