1970 Dodge Dart 318 piston rings

Well, with the 'significantly larger gap' issues you have found with the standard rings pointing to bore wear, then it's a no-brainer to bore and go to new, oversized pistons. Gaps will be right (though you need to still chekc and maybe touch up), ring side clearance will be right (no rings flopping up and down and wearing out in short order), break-in will be good, cylinders will all seal and operate right, and blowby will be normal. I haven't done a no-bore rebuild since 1978 after doing a couple due to limited funds and finding out how poorly some cylinders operated afterwards. Proper bore and piston fit, and ring operation, are fundamental to a good running engine.

Let me ask, when you say 'significantly larger gap', how much larger are these gaps vs. the upper limit?

Is this a rebuild for performance or just stock?