to make a lsd axle for a g20 you need a b13 short side inner and shaft.
use the g20 outer/
the procedure is easy, you need a big hammer gloves and some greese with good boots.
take the b13/b14 axle with a big hammer and hit off the outer (the part that goes in the hub) do the same on your g20 axle. take the g20 outer and slide it on the splines and slam it over the circlip. Use the nut on the threads if your going to slam it on the ground so you dont damage the threads. Say hello to your new axle
i been doing this for years with no problems because no autopart store ever has my axle