The GM cranks are 1038 steel the sam as the forged rods and we use to use them in the circle track engines we build and with the small radius thre seem to be signs of cracking after a season of running and I have seen some break. And the indexing on the GM cranks is all over the place.
The GM forgings we use come from Crower or King's crank in NC with a 1/8 radius and those cranks seem to hold up fine and they are indexed.