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If you're doing serious towing or getting near 500 hp you'll want 4-bolt mains. There's no way to tell without pulling the pan and looking at the main caps because 2 and 4 bolts are both machined from the same block casting. If you're going for all-out power, it's better to start with a 2 bolt main block and have it machined for splayed main caps, but I don't know how much a machine shop charges for that.
A factory 4 bolt is weaker than a splayed 2 bolt block. Then again if you are getting to the point of needing splayed caps, better to go with a Dart SHP block and go with a 4.125" bore. After running all the $$$ for my 383, I could have had a 415 for not all that much more.
My 383 would have been just fine as a 2-bolt but I happened to start with a 4 bolt block.
I know it’s been almost a year since the last post on here but did you build this yet? I have a 97 c1500 and I’m leaning far more towards the 383 instead of an LS swap. With them both being in The 430hp range I haven’t heard why one is better than the other. Only thing I can think of is because LS needs a Frankenstein wiring harness or stand alone.
Both in the 430 horse range, a 383 will have substantially more low-midrange torque than a 6.0L cammed up to make the same power. Without boost a LS is pretty soft on low-midrange torque which is what gets a heavy truck rolling.
