So need to take the old 427 over to the machine shop, but I'd say is a good chance it won't clean up at 4.250". The ring selection at 4.255" and 4.26" is not nearly as good. Of course can get a some moly rings in a 5/64", 5/64", 3/16" ring package, but would like something more modern since will need a custom piston anyway for that bore size.
I see three 1mm/1mm/2mm sets available
Mahle RING SET 4265MS-112 which is a ductile iron moly top, cast 2nd. for about $260
Total seal AP Plus CWC1124260 which is a coated steel top, ductile iron 2nd. for about $285
Total Seal AP Plus Gas Ported Piston Rings CWC1124260GP which has a fancy gas ported coated steel top ring, ductile iron 2nd for about $380
So other than the cheap 5/64" tractor rings which would you guys pick? I'm thinking the total seal AP worth the $25 over the Mahles. The gas ported rings TS says makes more HP via better seal, but have not found any real data to back up that claim.