['ol Pinion head]

Originally Posted by 79 Phoenix

I'm thinking it is because the block is a 557. It looks like the smaller one to me 2 1/2".

Originally, the 500557 400 blocks used the 2.75" register cranks. That practice lasted at least a year/ well into mid '76 engine production. Later '76 model 400 blocks received the smaller register cranks, do remember checking a few.

For many years i had a Pontiac V8 engine core program going. On occasion I would pick up '76-78 500557 shortblocks, then simply shell them out for the good condition smaller register 400 cranks, as well as oilpans, timing covers, valley pans, & hardware. Two of the '77 500557's I stripped down, the stock cranks had the correct recess for a pilot bearing. Both of those cranks were needed in 4speed W72 TransAm engines where the owner had spun a rod bearing & was still wanting to run the stock small register 11" cast flywheel.