Re: 14SF to 14FF conversion
Any FF out of a 3/4 ton will bolt right in.
A 2 wheel drive one will require that the shock mounts be relocated but that is all.
Depending on what size the u-joint is is another factor.
If the caps on the yoke end are 1 1/16" it is a 1310 and will use a NAPA# 338, a cap that is 1 1/8" is a 1330 and will take a NAPA #447, 1 3/16" is a 1350 joint and will bolt right in.
If you do decide to do this you will also need new u-bolts.
$10ea at most spring places.
The axle tube diameter is 3 3/8" on a FF.
Even if the tube is the same size on the SF I would not reuse them, once the u-bolts are torqued down they stretch and it is a bad idea to reuse them.
I am not sure how the e-brake is routed on an 85 but on my 78 K5 the cables hooked right up.
78 K5 3/4 ton, 305, SM465/NP205, 33x12.5 EXT's.
No lift yet.