A run of 15 classifies it as a 'pilot run' car, but the intent was to introduce the supercharged engines to NASCAR. These cars would not have been built on the regular assembly line, but in Ford's Pilot Plant.
In 1957, Ford was 'tooled and building' FE engines for the '58 model year. The all iron, 625-lb., Y-Blocks were four yrs old, but 'in production'. Classic Birds were in their third and final year for that body style with the 312 engine.
Ford wasn't spending more money on a project to make this car fast. After deleting the radio, heater, and anything else Ford could shed, the final weight was 3,300-lbs. with a single carb and a (inexpensive) stick shift for better control and more weight savings.
So Ford added a Paxton Supercharger to instantly give 40% more HP. BTW, Paxton's were the cheapest and easiest (centrifugal) superchargers to bolt on.
We go by Horsepower:Weight. This engine produced ~300HP with the supercharger but it was bogged down by 3,300-lbs. of full frame under a steel body. It ran an unimpressive 17-seconds in the quarter mile. Regardless, it was something new, different, and rare.
I love the Classic Birds for what they are, but I'm going to get an awful lot of PM's here because in my opinion, they were too heavy for serious racing. For 1958, Ford quickly dropped T-bird's full-sized frame, (little 300-cube) Y-Block, AND the supercharger, in favor of the FE engines. Ford never looked back. Without superchargers, FE's produced more HP and easily beat 17-seconds in the quarter. Full size Ford (and Edsel) cars & trucks retained Y-Blocks until ~1964. Argentina and Australia kept them much longer.
All rare classics are worth big bucks IF they are kept bone stock. These supercharged T-birds are garage queens that should never be driven on today's roads. Trailering is the only option, not because they are fast but because they were built for 1957 traffic, when most cars were two-tons. They are dangerous in today's (light/nimble-car) traffic.
Yes, Ford found improvements in the original Paxton's and offered a SB to 'correct' the original 15. If I had a Phase-1 back then, I would certainly do the Phase-2 upgrade.
Hindsight is 20/20: I suppose if I had an original Explorer w/self-destruct tires, it would be worth a bundle to someone (but I wouldn't put my family in it). Sorry for being so cynical, but my idea of enjoyment is to drive my classic cars to shows and cruises on today's roads with my family inside. All the spectators love it too. - Dave