I've got my car (see my signature/profile) back on the road (still lots to do, though) and I installed the Shelby mod. Someone posted a week or so back about this and stated that the mod is not fully effective unless you install some other modifications. Stiffer and drop springs were one of those items. Other items were a large (1" or more) front sway bar, rear sway bar (5/8 or more), gas shocks, wider tires. I did this mod after I had previously had the other items (I also cut another 1/2 coil out of my Magna 620 front springs, hehehe). The car didn't drop too much (if any) after installing the Shelby mod.
However, your original eye rear leaf springs will most likely be too high for the lowered front. I am running Torq-Thrust D, 15 x 7 wheels, with Nitto 460's (unidirectional, good for dry, which is perfect for Socal) 225-50-15 tires. They fit in the wheel wells nicely after all of my hacking.
Good luck...
Steve Leslie, 65 coupe in restoration. 302, toploader, A/C, disc brakes, bench seat