455 Block ID guide
Here is a comparison of early model big block Buick blocks.
The top drawing shows 1967-72 blocks with the round water port above the
cylinders. The lower images show the later model blocks which have the oval
water holes and appeared sometime in 73-74. The later model blocks 1975-6
are slightly better cast than earlier versions and have the improved oiling
passages that first appeared in 1971.
Here is an actual picture of a 73 455 block with oval water
The only head gaskets that are year specific are the shim
steel gaskets. You can not use a steel shim gasket on 73-76 blocks and heads.
Felpro as well as other brands are for all year big blocks, 400-430-455.
There are two different intake valley pan gaskets 71 and
earlier and 72-76. Use the valley pan for the year of the heads.