[Mr70]

I think this rod would work in all applications,as Bill & Greg have stated.
But technically the #3963552 rod was a brand new part released new in 1970.
The #3969804 was released later and was considered the fourth design by A.Colvin.
His Quote on the #3969804 rod:
"The last big block rod design with the same forging as the earlier L88 rods,but this rod has the 7/16 knurled shank.This rod was not quite as strong as the L88 rod,but it is much heavier then the Std. 3/8 rod."