Dunno about that, the info I've seen does not support the claim the 413 and 426 blocks have the same casting numbers.

Cap designed changed for 74 MY blocks. Main saddle designed changed early vs late as well.

413's have a interesting history, early pass car stuff vs later industrial/HD truck useage.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.