I sas my 89 with a 1983 axle and have a welded front diff with Marlin inners outers and marfields. i shimmed my knuckles just right but when the hubs are locked the tires only turn half as far as they should.
Is this because of the welded diff? Would a limited slip fix the problem. Or is it something else? I think something is binding.

 

Turn as in the wheel/tire rolling forward/backward or turn as in steer from side to side?

If binding while steering, open the axle up and figure out what is going on. Locker/spool, limited slip should make no difference in steering angle. Might be the birfields are missing a snap ring or two or something like that.