From DE:

"Also the jugs have worn a taper at the upper end, normal repair is
bore oversize, use new piston. No way am I paying $116 each for new
pistons on this beast."

The old way is bore out most of that taper and knurl the pistons, isn't
it, to reestablish the fit?

I've never done this... I gas-ported a small engine piston once. You
can buy oversized rings cheaply and grind the gap with a gap grinder to
make them fit the new bore.

It has something to do with piston slap, I think.

--Doug