Speedo/Rear End question...

[firefighter736]

Hey guys... just found out that the leak I've been fighting for a week or so is the oh-so-famous Speedometer housing leak.

I had previously thought I had bought the truck with a TH350 in it only to find, after ordering a Speedo Bullet, that I have a Olds TH350 and share the same speedometer housing with the 700R4.

The speedometer has always been off on this truck so I figured that now would be the time to fix it. The big question is what kind of rear end do I have? I don't really have time to pull the cover off the rear end and count teeth (I would like to get the Speedo Gear/Housing/seals ordered tonight) so I was hoping someone would know the gear ratio for the average '66 C-10 with an inline-6 and 3 on the tree. I know this is probably asking for a lot (I'm sure there are many variables...) but it's worth a shot.

Edited to say I've heard most of these trucks with the I6 had 3.73s but it seems to be taching so high that it makes me wonder if 4.11s came in them, too...