All the three freeze plug 400's ive came across were 4bolt mains. The two freeze plug 400s were two bolt mains. The old school drag racers wanted the two bolt main two freeze plug engines bc they were pretty much identical to a 350 on the outside, the cylinder walls on the 2 bolts had more beef towards the bottom than the 4 bolts did, and the block had a higher nickel content and would last longer...
Just a little useless information that ive heard over the years
You're right about the 2 bolt blocks there is more beef where the mains lead back into the block.Alot of 4 bolt blocks will crack there when you start making some real power.We always just put ARP studs in the 2 bolt blocks, and never had an issue.