My regular cab long box 89 F250 had a D50 TTB in it when I bought it, leaf sprung of course. The ride was awful. With F350 suspension and a D44HD straight axle from a 79 F250 the ride is much improved.
The suspension actually moves when you hit bumps and the truck doesn't lurch like it did when you hit pot holes with the D50 TTB.
As far as I'm concerned, OP should throw that TTB axle in the scrap pile and get his choice of solid axle, D60 is much more straight forward than the old D44HD that I put in.