Back when there were lots of blocks available to whittle on, 30 or 60 over was the preferred choice. The engines with an 80 overbore were sold mail order by places like J.C. Whitney, Sears or Montgomery Ward, with a fairly short warranty (or none at all) to people who wanted to keep an old beater car or truck running a while longer. As usual, the skill of the rebuilder and his attention to detail had more to do with the quality of the job than specific over or undersizes. 30 under crankshafts were also relegated to short life, low cost rebuilds as well, with standard, 10 or 20 undersizes preferred. The stroker shafts I have in mind for the engines I'm working on will have rod and main bearing undersizes approaching 1/8" below "standard" shaft sizes, so as long as bearing clearances are correct on the resized shafts, original diameters can be ignored to some extent. Stovebolts were WAY over-engineered in a lot of places, compared to more modern engines.
Your high mileage 60 over block might be a very good candidate for conversion to slip fit flanged sleeves, if you can find a machinist willing to think outside the box. That's exactly the situation I have in mind, to save blocks that might be scrapped otherwise.
Jerry
