I am fairly sure that the blocks have the same bolt pattern between the two, the difference is between the turbo patter on some blocks for the turbo 400 auto.
I'd say that the bellhousings are the addaption to the block between auto and 4 speed.
So if you want the 4 speed you may need to stay away from the turbo pattern blocks.
Please correct me if I am wrong.![]()
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