the early '72/''73 "cold weather" blocks were supposedly the best of the 400's. Part number ends in 230 I believe. Had some thicker side ribs. Whether it's really stronger, who knows.
The early 230 blocks look really nice and have big beefy mains but the cylinder wall are not any thicker than other casting numbers. I spent a bunch of time finding an early 230 block years ago because I had heard that it was "the one". When we sonic checked that 230 block we found out it was junk. All of my money and my dreams of a killer block disappeared in a poof.
I bought one of AndyF 230 cold weather block and sonic tested it, it was no better in the cylinder walls than any other 400 block I have tested
OP, I shoot for a minimum of .160 after boring on the major and minor cylinder wall thrust surfaces, the block side and the cam side
That has work so far up to 800 HP on race gas and a little more on E85, I do replace the main caps also do to a friend breaking one in a 451 C.I. 400 block S/G motor years ago making close to 750 HP and using old race gas in his Super Gas car
I have bought three race blocks, high nickel Koleno, KB aluminum and the last one is a Bulldog cast grey iron. These will be used for a Hi Po build, north of 900 HP N/A
I have cracked the main webbing in three RB blocks before switching too the 400 blocks to make sure I don't run over a crankshaft
