I do believe it is the original rear end so its probably 4.56s. The tires I have now have an overall diameter of 27 inches. According to the link HOT ROD gave me that would have me in 4th gear with RPMs at 3689.

I would like to land somewhere in the blue or green range by this diagram: http://www.sierrabronco.com/TireGearRatio.htm

In my opinion 4.56s are not necessary for me and keeping it original is not an issue either.

Longbox suggests I could easily go with 3.73s, is it possible for 3.21 3.31 3.42 3.55s or would that be unfeasible to do?