4-Door with 340 from the factory?

YY1 said
Olds 350 400 and 455 is the same block.

...but head gaskets would be different.

Same basic structure, definitely NOT the same blocks, deck ht is way taller on 425-455. 350 is also not the same block as 403 which has siamesed cylinders and 1/2" head bolts.