I have the same question and hope it gets answered here. So far the history page on Arkus Duntov notes that up to the 327 SBC there were only two-bolt mains in the block and it says that the need for a four-bolt on the street is exaggerated EXCEPT FOR TOWING!. Also in the book by David Vizard "How to Build Max Performance Chevy Small Blocks on a Budget" the No. 3 buildup he shows reaches about 380 H.P. and he comments that a two-bolt block would have been adequate. Then there are the Milodon angle-bolt main caps which convert a two-bolt to a four-bolt with added bolts on an angle. That means an added $150 for the after market caps and added line boring charge. From What I have "read" it looks like a two-bolt is OK up to 350 H.P. unless the engine will be involved in towing. Who can tell about a two-bolt failure and the conditions of that failure?

Don Shillady
Retired Scientist/teen rodder