The simplest setup would be to use the original leaf springs or possibly update to one of the single-leaf spring options if you don't intend to use the vehicle like a real truck, and use a Panhard bar for sway control. A rear anti-roll bar might be worth considering. Other than impressing onlookers with the cool factor, I don't see a good reason to use a Watts linkage or one of the other pivoting bar and heim joint systems. Those things have a legitimate reason to be on sports cars or round track racers- - - - -reduction of unsprung weight, also the reason for independent rear suspension and a frame-mounted Jaguar differential, but it's unlikely a vintage pickup is going to see much of Laguna Seca or Watkins Glen, or the road course at Daytona!
Jerry
