I got lucky and found my 4 bolt 400 in a 1970 Impala with a blown tranny for a hundred bucks.
I was also told by a racer I know that he prefers the 2 bolt blocks because the bearing webs are thicker and you can have splayed 4 bolt girdles installed.
But if you have to have a factory 4 bolt 400 look for a casting #3951511.
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