If you have breaks amywhere on your car you need to fix them! If you have drum BRAKES on your car and everything else is reasonably good shape, ungrading to one of the 73 and later disc brake setups is just about the single biggest thing you can do to improve it, especially in the bang for a buck category. Once that's done high quality aftermarket shocks would come next followed replacing the rear springs with brand new replacement ones (as opposed to re-arching the old ones). Replacing the ball joints and every bushing on the car with new ones would be the next logical step (urethane on the strut rods even if you stay with rubber for the rest.) Do a freshened up steering box next (Stage 2 Firm Feel for me). Only after all that would I worry about stabilizer bars and brick bat sized torsion bars.
I found a late 80s Dippy in a pullapart last year and got everything I needed (upper control arms, uprights with balljoints, rotors, caliper brackets and caliper, and all the fasteners, even got the hoses although I'm not going to use reuse them) complete for $45.00 a side. Even if the Dippy had a 2 bolt master you can buy a bracket to use it. You can use the proportioning valve too.
That same Dippy could have donated it's 8 1/4", 4 1/2" bolt pattern rearend, shackles and shackle plates, had I needed it, although I can't remember if the spring perches would have needed to be moved.