383 block strength?

383's comparable to the 396, 390 Ford, 390 AMC, 394 Olds, 389 Pontiac.......I'm sure I'm missin some.

100% correct. The part you are missing is the succession of those engines, related aftermarket parts and modern technology. For example, the Chevy small block started it's life at 265, then 283, 327, 350, 400 and now lives at 427 cubic inches in a block that will happily live at 1,000hp. Similar can be said for mopar.