My original numbers engine is 30 over and I intend to build another engine and leave my numbers engine in good running condition.
An after market block and rotating assembly is the way to go in my view. It cost a bit more but 500HP is easy and you have a nice relaxed engine. Besides, I worry about my gearbox getting soft above 500 ft lbs.
Personally, I would stop at first bore on a numbers block. If something bad happens on an overbore you will be buying a new block anyway and your original is now gone. Just skip that part and go get the other block now and slide your original under the bench.
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