Another question for you guys. I just picked up the 3:55 posi for my 66. I was wondering if any of you could tell me the correct speedo gear for it or if you could point me to the easiest formula for figuring it out. It is an automatic, and I am running 14 inch wheels with radial tires.
Thanks

Here's one of the many calculators out on the Web.
http://www.mindspring.com/~steveflyer/speedo_gear_select.htm

Once you pull the speedo cable out of the trans, you can peek inside to see the color of the drive gear to help with your selection.