LOL! I remember that situation well, since we were forced to modify the block to use the early style main bearings, or wait a week or more to have the "right" ones shipped in! Now John's 261 can use either style of bearing if it ever needs to be rebuilt again. Chances are that will be the "next guy's problem", unless I discover the Fountain of Youth in the next few years! Regardless of what the casting numbers and date codes suggest, nothing beats a forensic inspection of what's actually there! Lots of things can change over 60 or 70 years' time, no matter what happened at the factory.
Jerry
