While the numbers tend to look good for "no unusual wear", are the bores round? Looks like the pistons are still in their holes? The older service manuals used to mention using a "ridge reamer" to get rid of that upper ridge in the cylinder walls just to get the pistons out.
What you're seeing is just the top of the cylinder bore, but with no vertical marks, probably no scoring on the piston skirts.
Consider that the bore taper is a wear issue, although it can still be "in specs", but that when the engine was originally built, there was no bore taper.
So, what is the orientation? To just "ring and bearing" it, to do a minimum over-bore with new pistons/rings/bearings?
In the "normal machine shop" world of small block Chevies, it usually took a .030" overbore to get the bores cleaned up, just into "new metal". This non-tapered bore would make things work better for longer, with good machine work. Easier to gap the rings, too.
But, from what I've seen, getting new pistons for a B/RB engine that will accurately match what's in there can be difficult. First thing is that in the later '80s, many piston manufacturers lowered the piston pin location about .020" to help decrease the mechanical compression ratio to better work with the lower octane fuels as had then. A minor thing to me. Then it seemed that as some of the older piston makers vanished, most of the B pistons became more generic in their specs, trending toward 2bbl specs ( or lower CR) than 4bbl specs for 4bbl motors. Have to really check the casting number on the bottom side of the factory pistons to see this. That's with the normal cast pistons (which is what was in the engines from the factory). If you want to go to forged pistons, then things can change a bit, by observation, as that then gets into the NHRA-approved pistons for each engine, in the stock classes.
Cast pistons need a somewhat "tight" skirt clearance, but forged pistons need to be looser due to their greater expansion from cold to hot. Hypereutetics are supposed to be "cast clearances, forged strength", I believe.
If possible, I think I'd head toward cast pistons as they, being a bit softer, could be "easier on the block, as to wear", than the harder forged Hypereutectic pistons. Plus being a bit less expensive. Make sure they have the expansion struts near the piston pin, as the factory pistons did.
UNTIL you get the pistons out, don't order anything! You could well find that at the bottom of the ring's contact area on the bore might have a "wear area" that can reflect the "start/stop" motion of the piston, possibly not unlike what you see on the top of the bore, just not quite so pronounced.
From the initial measurements you made, order rings for the smallest dimension, not the largest. Ordering for the largest would certainly mean that you'd have to gap EACH ring to ensure that when it collapsed as it encountered the smaller dimensions, THAT's what the ring gap would need to be set at so no binding might occur, lest the ends of the rings touch in that spot of the bore. NOT a desired situation. If you ordered for the min bore size, with each ring gapped to that dimension, then ring tension might open up the ring gap at the top of the piston travel, which could lead to an ineffective seal, possibly. As it is, when the pistons/rings were installed at the factory, they were all gapped the same and the wear situation is something they've learned to accommodate with time "together".
IF all you're wanting is to just put rings in it, with nothing other than a dingle-berry hone job, than get a machinists rule and insert EACH ring to the bottom of its travel on the cylinder wall and set the ring gap THERE. This should ensure that the rings don't end-touch in that area, but still use their spring tension to maintain some contact at the upper end of their piston travel. To me, THAT would be the best way to do things.
As for what was in the parts books, the "Std" or .005" OS pistons were usually used for warranty repairs where the cylinder was not damaged. If it required an over-bore per se, that work usually went to a trusted machine shop to be done OR a warranty replacement motor was procured from Chrysler, typically.
Using the existing pistons would also mean that the rotating assembly would not need to be balanced. Most aftermarket pistons are heavier than the stock pistons, which might mean the engine would need to be balanced to the new pistons, for best results. In that realm, there are also "Over-balance" and "Under-balance" strategies, depending upon what rpm range the engine will live in. So, keeping everything at "factory balance" would be good, if possible.
How do the crank journals measure out? Plastigage can work well, here, rather than using mics.
Many years ago, a friend had a C-30 Chevy 2-car hauler truck, 454 of course. He was getting some oil consumption, so figured it was time for a rebuilt, but when he took the heads off, it all looked pretty good. At the recommendation of our machine shop associate (who'd built the particular engine years prior), he put "chrome-moly" rings back into the engine. NO re-hone, just put them back into the existing bore surfaces. Which worked just fine. IF it hadn't, we'd heard grumpblings about having to do it again.
The "chrome-moly" upper rings are a chrome-surface ring with a channel of "moly" in the middle of the cylinder wall contact surface. Chrysler used them in many of their HP engines in the later '60s and probably up into the middle '70s. The moly, in addition to being a non-wear substance, also is allegedly porous enough to absorb a bit of oil to ensure that top ring has some lubrication during extreme use. Plus, it needs a slicker bore surface to work with than a normal chrome-faced ring. So, with the used bore surface, it worked just fine.
IF you do use the dingle-berry hone, DO ensure that you match the factory hone pattern, with the specified angle between the cross-hatches.
Be sure to use quality gaskets. even if the head gaskets might be "composition" gaskets of .040" compressed thickness. For a stock rebuild, don't need anything really fancy, just good stuff of at least OEM quality.
Enjoy!
CBODY67
