Reply to "Suggestions for chassis stiffening kits?"

Beside the various vendor kits, there are a few other ways to stiffen up a unibody car like the Pantera. The earliest way known to be effective is to seam-weld every spot-welded joint in the car! (GR-4 LeMans cars had this done) Obviously this will not appeal to those with 5-figure paint jobs already in place.
The second, mostly-unproven way is to use under-floor joining-sections and gussets between the floor panels and the front & rear subframes, ala Mustang stiffer kits. I think this approximates some of what the Vendor kits do.
The third way, as someone mentioned, is a full cage welded, not bolted in place. A bolt-in rollover hoop behind your head will not be as effective, even with dual down-leg braces.
FWIW, Larry Stock of PPC-Reno has his own front & rear brace-kits on his do-everything '72. After 5-6 years of Silver State events including getting 'big-air' at 150 mph over a hump-backed bridge in one event, he completely cracked the lower front subframe extensions off the tub! Daylight was showing clear around both sides, which mount the lower a-arms and front swaybars. But because of the structural rigidity added by his lower front brace-kit, he only found out about the breakage when he took the car in for a wheel realignment.... So while the stiffness benefits of an upper-front brace are debateable, the LOWER front kits do perform a function!