ok ...I took a long hard look at a known '75 block, next to a six bolt block. Here are the diferences:

75:
has deep water drain plug casting

has what looks to be a date stamped on oil filter side of block on the bottom. It says: 75 1 22

has a tapped hole on dizzy side of block just to right of the dizzy and up a little. It is plugged. I suspect its a water jacket gauging the size of the plug.

has extra casting between 1 and 4 near the connecting rod opennings

the main cap bolts are metric

main caps are thicker

two tapped holes in a vertical fomation on dizzy side of block, towards the front bottom of engine (just behind timing cover) is metric!

the gears on crank and cam are a different pitch. In other words, I can't interchange timing gears between the early and late blocks, although either will work in either block if you keep the joining pairs together.

and here is a really odd one: the little bolt that holds the clutch folk in one of my bell housing is metric and another is not, though I thought they changed the design of the clutch folk when they went to cable from hydro.?


pre 74:

opposite of above..meaning all listed is either different or doesn't exist.

Tremmelle