L31 or L31R Crate engine question

[reloder28]

I have a 98 Tahoe. It has cracked both heads within 30,000 miles of the first mishap. Decided to buy a crate motor & have narrowed it down to GM #12530282 or 12530283. I can't tell the difference except the 283 is a four bolt main.

Is there a meaningful difference?
Will the new motor have the same head cracking problem?

 

[SunlitComet]

think the difference was the exhaust valve seats in the hd 4 bolt main from the factory were to hold up better to high loading by being pressed in. the standard l31 had machined surfaces integral to the head. and far as valve sealing ability i don't think it will make a difference you would notice at all. if they crack so soon i would suspect something else is wrong but new gm complete heads are available for $300 each.