Ford had some funky stuff going on with their axles.
The F350 used a dana 70 rearend until the 10.25 sterling was released, EXCEPT for '79 F350 4x4's which had a 30 spline dana 60 rear.
some F250's also used the D70 into the 80's, usually the 70u.
The F350 4x4 had a HP60 in '79, then in '80 got the d50 ttb. in '85 or '86, the HP60 came back (so we still have hope for Chevy, lol). They switched to balljoints in '91.5.
IIRC, all dually 4x4 Super Duty's have the D60. Then in '02, all super duty's got the D60.
Somewhere along the line, they switched from the 10.25 to the 10.5 rearend.