Your questions reveal some basic misconceptions. Pistons do not "drop in."

New pistons and block go to the machinist so the bores can be sized to the pistons. If you are not sure what size, get the block to the machinist first to get the necessary oversize figured out.

Next, boring to increase engine size is not profitable in Mopar engines, because casting quality (core shift) varied substantially in all the years. More to the point, a sonic check is very much what should come first to see what cylinder walls your block has. Boring the 426 to 440 size is something I'd never recommend.

The corollary to this is that stroking a B/RB is so easy and can be done for large displacement increases.

Now on to the bores. If there is a ridge there is almost certainly wear in the bores. Reaming the ridge is a very hazardous operation for the novice. It is just too easy to cut too deeply into the cylinder to the area where rings need to seat. The area of greatest wear in the cylinder is where the rings are loaded the highest, at the upper end of the cylinder.

If you want to keep the standard bore and not mess with the cylinders then the used set mentioned above is a good choice.

Imho you'd be best off having a new set of pistons made by Autotec. Then they can have the compression height, valve notches, any dome, etc exactly to optimum.

R.