According to race bulletin #8, July 1982:
"The early 360 ('71-'76) blocks are a special case. They use a 4.00" bore (340 was 4.04") but the block was made with the 340 water-jacket core. This means that these blocks can be bored to the same actual bore size as any 340 and have the same borewall thickness. This is NOT true of the newer 360's"
The thing is, that's only 20-thousandths on the radius even if it is true. That's just not really significant if you start measuring and see how much the numbers vary place to place. I can't see how they'd even bother to have a different set of water jacket cores for such a small difference.
