New Rear Differential; speedometer off

[Shawn's 78]

I took the plunge and swapped out my 3.36 gears for a set of 3.70. Since most of my driving is cruising, the few hundred extra rpm's on the freeway don't' bother me much.
Except that my speedometer is now off. Showing 70 it is actrually 60 (using GPS).
I have a saginaw tranny, so which speedometer gear do I need to swap out to correct the MPH? I see that Eckler's sells them, but I can't find a guide or formula to know which one to get. :W
Help!

 

[SnakeOiler]

Let me google that for you

 

[Vettehead Mikey]

Your AIM will also have a chart that shows the correct gear combo.

 

[Shawn's 78]

My AIM manual has only odd pages from 17 on (go figure!). The specs for Standard Trans is on either page 18 or 20. Anyone have copy? Or if someone has the correct speedo gear for the 3.70, can you post?