As I said, when I first got on this forum, it was common to bore early blocks 1/8 and they survived. Sonic testing, wasn't even thought of in the 60's.
Pull a soft plug and drill test it and see what you have if, a 1/4" drill fits tight, you'd have the same as a 4.25 bore, 427 (1/8 walls), w/o core shift. If a 9/32 drill fits, that would be the same as a 4.28 bore, 427 (.110 walls), again, w/o core shift.
But, my guess is that you'll sonic test it? If so, it will be interesting to know the result.
BTW, you didn't say if it also has the 428 dampener.