[LMSRACER]

O.K., I just checked Three Different Blocks for Dowel Pin Sizing.
1967 400 Block = 0.309"
1971 455 Block = 0.309"
1974 350 Block = 0.309"

The 1974 350 Block is the Newest Block that I currently have.
So, the Question is:
If Pontiac Changed over to a 0.3125" Dowel Pin, When did it Occur?

Regarding the Question on the IA-2 and MR-1 Blocks:
On an IA-2 or Mr-1 Block the Thickness Between the Bores at the Deck Surface is approximately 0.270" @ a 4.350" Bore. Therefore, I know that it is going to be Less than that at the Base of the Cylinder Bore. I'll bet that it is "Considerably" Less....

Larry S.