Machining the piston groove depth depends on ring radial thickness. This is a very precision machine operation. In my opinion unless you spend big bucks with area o Diamond,or someone similar you’ll have a mess. Better off just using your current top ring. The 2nd ring is basically an oil scraper. You could always just buy a set of 2nd rings since they look pretty worn. Your leak down didn’t look that bad. I’d run it.
Doug