something to drive the Corvair lovers nutz...

[Cyclone03]

thats what I told him....

[OldMachinist]

I'm certainly no expert but I have to concur with Continental's crank failure guy. That is a bending failure which means it wouldn't have been caused by undersize bearings. If that were the case it would have broken in the under side of the fillet. Nitriding is a surface hardening process that makes the bearing surfaces of the journals harder for wear resistance but does not make the crank stronger, in fact I would argue it actually makes them weaker as far as a fracturing type break. Did you know that the mains were bored from each end and on the first few the bores were actually offset? Instead of correcting the offset bore, Chevrolet made main bearings with one shell thicker than the other and they had to be installed correctly so the crank would be in a straight bore. If the main bearings were incorrectly installed an offset could cause a bending failure and I'm not insinuating this happened but it is something to investigate.
I would think you could get a billet crank made of contemporary materials that would be stronger and as to cost, how much does a billet crank for a fuel engine cost? The corvair would certainly have much less material in it and you would start with a much smaller piece of steel.