I'm pretty sure a GMC has considerably more wall thickness than an SBC:
1. it was normal practice at the time
2. it's a sound accounting decision (fewer blocks scrapped due to core shift, etc.)
3. extra weight is harmless in a truck chassis
4. more possible re-builds = longer service life
However, no "modern" V8 seems to work as well after about .060".
However, IMHO a comparo to a Chrysler 440 is closer (despite the bore size difference), because the long unsupported wall inside the water jacket is roughly proportionate to the deck height (SBC is 9.025").
The low-deck 9.98" B is preferred to the high-deck 10.725" RB for just this reason: wall stability.
IMO the large overbore trend of the 1950s is entirely due to a few factors now irrelevant:
1. "my Ford V8 accepted a big overbore without frequent failure, therefore I'm going to bore my Cadillac 3/16" as well".
2. "stroker crank? What's that?" Biggest motor wins.
3. bad ring seal, high case pressure, etc. were normal for not only rebuilds, but even some stock engines
An "ill effect" is subjective to the application: a street rebuild with 200 hp will tolerate a thinner wall than a 500 hp blower motor.
I realize you're in a tight spot - budget concerns suggest a specific bore size to avoid a cu$tom piston, so it's a compromise like everything else in motor building.
