If that is the 360 that came in that ‘71, that is about as good as you can get in the world of factory production iron blocks. The cylinders were cored on 340 T/A blocks and it’s possible that some of main webs may have come through with the extra iron for four bolt mains in the very early 360 blocks. Sonic testing is required beforehand, but most pre ‘74 360s have enough iron to easily handle 340 o.s. pistons and oftentimes beyond.
