F-250's came with either a D44HD or D50 TTB. Some people will say after a certain year, all 250s had D50s, however I have found both in the internet, and in junk yards examples of both, so to say an F250 has a 50 after a certain year is misleading. The easiest way to tell the difference is two fold:
1) D50 lockout IS a D60 lockout, and thus is ginormous; D44HD lockout is a normal D44 lockout.
*note: accompanying the lockout is the size of the hub centre, that is, the hub center of a 50 completely fills the centre hole of the wheel, whereas the 44 necks down dramatically.
the following pic is of a D50 and D60 hub and lockout, they are identical.
2) axle shaft u-joint retention; the 44 uses internal c clips, IDENTICAL to the D35 TTB, where as the D50 uses its own special u joints, and EXTERNAL circlips.
The D50 has a 9" ring gear, is HIGH pinion, and NOT 8.5" D44 size, (common misconception), and does 30 spline axle shafts.
The following picture is, respectively: D60, D60, D50, D44
Now, in terms of SPINDLES, the D50 and D60 are IDENTICAL in every way except one; The mating surface to the knuckle is 3/8" (roughly) longer on a 60, than a 50.
This is due to the caliper bracket being cast into the knuckle on a 50. However, this implies that you cannot SAFELY use a 50 spindle on a 60, as you would be depending on the studs to support the spindle. HOWEVER, you can use a 60 spindle on a 50, using a small spacer between the knuckle studs.
What this means is very exciting. Now, D60 OUTER shafts are equivalently longer than D60, to the difference in mounting surface. Thus, one can replace the D50 with a D60 spindle, and run 35 spline D60 outers and slugs
Centre Sections: As both the 44HD and 50 TTB used the same beams, this implies that the pig bolt pattern is identical; and it is. One can simply swap in a 50 centre chunk for a 44.
I will be doing this with my equalish length F150 D44 TTB arms, that is, running a D50 chunk in the D44 arms.
Now in order to run the D50 knuckles/outer/axleshafts, some modification to the D44 beams needs to be done.
The 44 and 50 utilize the SAME upper ball joint. The bottom ball joint, and position, are different. This is how I was able to make my front TTB axle in Rangebe...