I really think the best bet is to reinforce the stock K-member, add subframe connectors, and set the car up with 1" torsion bars, sway bars, good shocks, and some modern performance tires (NOT bfg t/a's). Probably have to go 17" rims to get decent tires in a good width/profile. With offset bushings, boxed lower control arms, and adjustable strut rods you can dial the alignment in. You can also upgrade to the later 11 3/4" mopar rotors if you've got (or get) '73 up spindles, it's a fairly cheap upgrade as its all stock parts and uses the same stock calipers. You just have to find the larger caliper brackets.
With the right set up, the "stock" suspension can handle just as well as pretty much all the aftermarket replacement stuff out there (ie, close to 1G on the skid pad). There was recently a comparison between a modern SRT Challenger and the Hotchkis TVS '70 Challenger, the TVS car pulled better numbers on the skid pan and beat out the SRT in a couple of handling tests. It wasn't far behind in the categories it "lost", and considering the changes in technology, that's pretty impressive.
For ease of installation and part sourcing, the Hotchkis TVS kit is hard to beat. But for the most part, you can piece together a very similar set up for less money.
