I've seen massive core shift in some of the 400 block castings I have tested, including both versions of the vaunted "230 and 530" blocks
Have yours sonic tested by a good shop first before going bigger than 4.380
The thickest ones I can remember using had the thinnest major or minor cylinder wall thickness of around .160 somewhere from the top of the cylinder wall to the bottom of the water jackets before boring
I would love to have a 400 block (I have two in stock now that need sonic testing ) that had at least .220 before boring as the thinnest part of the cylinder walls
I bought one 400 block from Andy F several years ago that only needed .007 clean up to get the bores straight, it was a cold weather early block that had been sonic tested. I retested with my Dakota 1000 sonic tester and the thinnest wall I found was above .160
I raced that motor four 4 or 5 yrs and took it out of the car last winter, I'm hoping to get it apart this winter to freshen it