Forget the traction bars.  All they do is make the car ride rougher, and do not completely stop wheel hop.  I speak from direct experience.  And Shelby even agreed.

Spend your money on a good set of heavy duty leaf springs, four leaf will do the job.  I prefer the reverse eye setup.   Approx $200

I wound up with a set of monoleaf fiberglas springs which do pretty good, but I still get a little hop if I turn all 500hp loose at one time.  Approx $450

I put Lakewood bars on my '66 fb. Still had hop with traction master style but the Lakewoods solved it completely.  http://www.ebay.com/itm/Lakewood-20470-Universal-Traction-Bars-/400280212922

I have the under rides on my car. Had trouble with spring wrap which caused the wheel hop. They didn't do anything to help. That said, they also didn't cause any binding. You have to install them when the car is at it's normal ride height. I installed the spring plate, attached the bar to the front mount and tacked the front mount while car was sitting on the ground. Then removed the bar and jacked up the rear to fully weld in the front mount. Looking at another design that pivots at the front of the spring and applies pressure to the top of the spring where the second leaf meets the top leaf, I added a clamp that goes over the spring at the same point and below the under ride bar. I just snugged up the nuts on the clamp so they only come into play when accelerating and the spring wants to flex upwards. Problem is solved and no binding nor change in ride quality.

I've never had traction bars because I added a leaf to my stock leaf springs and that eliminated any axle wrap.  However, my ride suffered.  Now, on the advice of John at Opentracker, I've cut that leaf almost in half and mounted it on top, as is done with a 4-1/2 leaf setup that many aftermarket suppliers offer.  Supposedly that will preerve much of the anti-wrap up capability of my previous 5 leaf setup, which is determined primarily by the stiffness of the front part of the leaf spring.  At the same time, I should be preserving much of the ride quality of a 4 leaf setup, which is determined primarily by the rear part of the leaf springs.  I haven't had it back on the road yet so I can't confrm that.

Part of the trouble with the Shelby under-rider traction bars is they are not the same length as the front section of the spring from the center bolt to the center of the eye, this un-equal length causes a bind that in turn causes the ride to suffer, when I built my traction bars I did pattern them after the Shelby under-rider's but mine are the same length so they act somewhat like a four link, even like this they stiffened up the ride a little so I then cut the bars and made them telescope, they have about 3/8th's of an inch before they are compressed and then they act the same as the under-rider bars, it helped the ride and I have no traction hop at all, I have  285/45 X 18's Nitto 555's on the rear that hook up pretty well when I hammer on the 427 so am really happy with the way the traction bars work. 

I have a '69 Mach 1 with Caltrcs they will solve your wheel hop problem. The R cars Shelby produced had the traction bars above the rear axle, the bar came through the floor and mounted above the pivot point of the leaf spring , no wheel hop.

Suggest you check a post on the old MS Forum; search "Traction Master Type Traction Bar Intallation Info" from April 2011.
I made a "Caltrac" set based on info provided by Kaz, and am still quite happy with the installation ... and no wheel hop.