Shelby "style" (ie: 65 GT-350) was a 1" lowered upper A-arm, 1" (I think) front sway bar, quick steer pitman and idler arm, specific springs front and rear,export brace and Koni shocks F&R. I may be forgetting something...
Boss front suspension was a different spindle with bigger bearings (used on 70-73 Stang/Cougar), specific shocks -n- springs, 15/16" (?) front sway bar, stock location upper A-arm, and 70 only, a rear sway bar (1/2">>???), with specific shocks and spring, as well as F-60-15's all around (roughly 235-60-15 today)
You can buy all of the Shelby stuff from any Mustang shop, Koni's are about $450-$500 for 4 (mine are 12 years old, and perfect), Springs are @ $70 frt, $150-200 rear, Sway bars @ $125. Lowering the upper arm is basically free, but you'd be best to install a Global West Neg Wedge kit to prevent ball joint failure. Of course, if your 35 year old suspension is thrashed, all the shocks and springs in the world won't cure your handling problems. A complete (I mean everthing) front and rear suspension rebuild would be a good place to start before you invest in handling parts. Remember, you can't build on a shaky foundation.