The probability is that the early 360 water jackets weren’t cored on just 340 water jacket coring, but the 340 TA water jacket coring. Unfortunately not the webbing, though. But the extra thick cylinder walls are for sure nice. I can confirm later 318 industrial blocks (Big capital “I” cast into the side), also have very heavy cylinders. They almost touch each other in the top third and only have an 1/8 inch between them on the bottom two thirds. I have yet to see any later year industrial 360s, though.
