jim4442

what is the difference in the early 455 blocks,ending in casting F vs the later ending in Fa?
thanks

RetroRanger

One thing other than the dates produced is that the later fa blocks may not have a thread hole for the four speed z bar

joe_padavano

There are actually four versions of 455 blocks, the san-serif "F", the serif "F", the FA, and the L. As noted the latter two typically (but not always) are not machined for the Z-bar pivot. Also, don't believe what you may read on line about the dates of use. I personally have a san-serif "F" block with a 1973 VIN derivative stamp. This motor also has KA heads and a manual trans crank. The head gaskets appear to be OEM steel shim (I have not pulled the heads), so it appears that these heads were born on this block. I'm thinking it might be from a 1973 V-code car.

cutlassefi

Add to that the later blocks are normally scalloped around the drain back area instead of having 3/8” or so holes.
And I’ve found the cyl walls in the later blocks to be every bit as thick as the earlier stuff, sometimes even more so.