SF stands for Semi Float. GM has 2 different 14 bolt rearends, the 10.5" ring gear full float, and the 9.5" semi float. The full float axle only comes in 8 lug, but the semi float version was made in both 6 and 8 lug. '88-'94 light duty 3/4 tons have the 6 lug version, as do '92-'98 1/2 ton trucks with the Z71 off road package, usually with the Sportside bed option. That axle will be too wide, especially if it came from a 4x4.
You mention looking into an S10 axle, those will be 5 lug, and will be a bit too narrow unless you get the 4x4 version, preferably from one with the ZR2 Wide Stance option.
