Josh i had similiar concerns and questions when i ran a 512 series 454 block at .125 over..with a 4.25 stroke crank it was a 511 or 512 for some if you round up .
Anyhow i was told by many people that this was too much Bore and it would run hot and most likley not hold up..then i had some say it would be ok..
i ran it and it done fine..ran at 185 degree's..it was PERFECT !.....a very strong engine..of course i did not spray any Nos and my compression was around the 13:1 mark
i think the only way to know for sure how much meat is left in those cylinder walls is to sonic test them and just see...and then your still gonna have people who think it may or may not work..
At a minimum i would sonic test Block being that it is so old..it may have some spots that are just too risky to try..
Of course the lil "m' Block is the best Route but its also a lot more Money..
if you can handle the Money side of it i would say upgrade Now,,cause i honestly believe your gonna end up there in the end..the same thing with me..i went back With Big "m" Block this last go around.
just my take on it.
Brian