Learn some more, Scratchhopper!

The 8 1/4 and 9 1/4 use the same length driveshaft. They have the same dimension from axle centerline to front of the input flange. 8 3/4 and Dana are different. Information from my old Direct Connection Chassis book.

R.

PS: The limited slip you have is the cone-type. You'll want to clean the housing carefully as it may have metal particles from the cone wearing into the case. I'd use a full synthetic 75W or 85W-140 gear oil with a bottle of limited slip friction modifier, I hear the one from your friendly ford dealer is a good choice.