We ran the Grocery Getter wagon for years with a stock block 455 and an N cast crank. 3 different blocks. After years and years of running around 1000-1100 HP. Zero broken or cracked N cranks. Ended up with 3 broken blocks. All cracked through the #2 main oil feed hole up to the cam tunnel. But our combination was a little different than yours. We had 5 billet main caps. Also aluminum connecting rods. But we ran it to 7500 rpms hundreds of times with a manual transmission and did 15-20 second 1/8 mile burnouts @ 7000 RPM's. Man, that was fun. IMO, with 4-bolt main caps, the crankshaft will be the last part to fail. Rods first, then the block, last the crankshaft. I have never run big HP with a 2-bolt main cap Pontiac. So can't help you on that part.
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