I have a max power phantom MP9 with a badly scratched piston I know they're Novarossi based I was wondering which one they were based off of I'm thinking it's a keep on. The motors were made several years ago like 2014 but has a nicely modded crankcase and a three tungsten weight crank. Would like to get it running again if anybody has any ideas as to what would fit.

Original MAX? MAX isn't out of business, high chance even the new AAC P/S set will fit.

But you have to look at the bore/stroke, Max engines ar so far I know always 16.2x16.8, the Keep-on will not work.

My piston Mics out at 15.86 which is a long stroke I believe. My newer RP9 pistons are much larger and won't fit in the cylinder.

Also the index pin in the case that aligns the cylinder is in the side, not at center of exhaust like RP9. I believe the keep on is on the side is why I thought they might work. I'm really looking for a P/S.

You are right, it is an xtra long stroke, also recognized by the side center pin. The model was released 10 years ago...
Then you will come to indeed a Keep-on, Mesphito or Mito-9

Would an Ison work?

.

No, the ISON is a normal long stroke (16.2 x 16.8)

Gotcha! Thanks!