Restore, Repair, or Maintain
If you're satisfied with your '73's original suspension, then replacing worn-out parts with direct-fit OEM-style replacements makes sense. These parts are going to be the easiest to install, and won't require additional modifications. They also keep your classic Mustang period-correct, preserving that perfectly restored look many aspire to.
If you're interested in more of a restomod build, then your options really open up. Lowering your Mustang is a great way to improve the handling and get a serious appearance boost. This can be done with lowering springs, coilovers, or an air ride suspension.
If you do lower your Mustang, you may want to look into a bump steer elimination kit. With a bumpsteer kit, you'll stay in control despite bumps in the road.
With an updated suspension, you'll be enjoying your first-gen Mustang for years to come.
Wrong year? Check out these first-gen years: 1964, 1965, 1966, 1967, 1968, 1969, 1970, 1971, or 1972 for additional options.