Slightly off-topic, but the V8's that came originally with Powerglide transmissions also have the oddball counterbore. Of course, if either engine has ever had a "crankshaft kit" installed, all bets are off! There's no telling which core crankshaft was used for regrinding.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!