All the stock RB blocks are a lot thinner in the main webbing under the cylinders down to the main bores than any of the stock 400 blocks made
I've heard of a lot more 400 blocks having severe core shift than the early 440 blocks but when you crack a cylinder wall or the main webbing that block sis toast, correct?
I would much rather crack a cylinder wall and have that cylinder quit working and find it right away than end up running over the crankshaft due to the main webbing falling out on the track or on the road
I've had one 426 M.W. block crack the main webbing and seen several 440 blocks that had done that also, no 400 blocks crack the main webbing so far