KB237's are the pistons you want. Have the block squared and milled so the pistons are all at zero deck and you're in great shape if you want to build for quench. If I was going so far as to rebuild the bottom end, I would spring for a set of edelbrock rpm or 440source stealth heads. Aluminum, closed chamber for quench and good flow, you will be able to run it on pump gas without problem.

I see you saw the smogger 440 thread, so you already know you can run 12's without touching the bottom end. If you do the bottom end and build for at least 10:1 compression you should be running 11's if you can get traction.

FWIW if money is an issue(isn't it always...?) I would be inclined to just go the bolt-on route for now. Your low mileage motorhome bottom end will happily do the job for the time being. You can still give the motor a paint job, regasket it, do cam, intake, headers and do valve springs and seals on the heads and have money left over to take a look at stuff like rear gears, limited slips, transmission issues, etc.