As Freddie said, a 2 bolt block is fine for street use. Find a 2 bolt 512 cast block and they are the same as the 4 bolt. I bought Freddie's 427/390 engine last year for just this purpose. It is standard bore and with a forged crank. The cast cranks and low performance rods were the main reason 2 bolt engines blew up at high rpm, not any fault of the block. Build the internals properly with a 2 bolt and you won't have any issues.
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Mitch
1970 Chevelle SS
1966 Chevelle SS
1967 Camaro ss/rs
1938 Business coupe, street rod
2000 FXSTS, original owner, 13k miles
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