Sticking rings is a very good possibility, especially with the older oil with limited/no detergents used in years past, and the car perhaps sitting a bunch. So, continue with the clean up. It may still be a worn ring/groove/bore, especially in #1 and somewhat in #6; the end cylinders run cooler on an inline 6 and tend to wear faster. I had over .020" wear on #1 versus under .010" on the rest.
Interesting way to do it with the MMO. You may also be freeing up a sticky valve guide; the stock valve springs are pretty low pressure so the /6 stock valves stick kinda easily.
You can do a simple crank polish at home. Cut strips of wet-or-dry sandpaper the width of the journal and long enough to wrap around and overlap the ends. Then double wrap a long leather shoelace around the paper and rotate back and forth, moving the leather from side to side of the journal to keep wear even. 220 grit for faster work and 400 for a fine finish. I have taken .001' or more off with patience.
The need to bore is for taper and out-of-roundness in the cylinders; you won't know 'til it is measured. And you should get the ring ridge out, especially if new bearings are going in.
New cam bearings are a very good idea. I got the same machine work (less crank polish but with piston R&R and 6 valves done for around $450 at a great shop so maybe you can find better pricing in your area too. (But I live in a pretty rural area where things are cheaper than in the big city.....)