Moparite is 100% correct. If you Lincoln lock your spider gears (weld them) you get a spool not a posi so that won't work very good on road and you'll just end up breaking axle shafts and drivelines. Save up your money (Don't get that pizza or movie once a week, put that money into a coffee can) and when you have the funds get a REAL posi diff. If you really want to do it right get one for each end of the truck.

 

detroit truetrac. love mine on and off road.