There were about 15 "D" birds that had the first version of the Supercharger on them before they started putting the "F" on the Data Plate. It seems that there was a subtle difference in the two Paxton Superchargers that were used.
I think I have that stashed somewhere or maybe in the Restoration Manual. I'll see if I can dig it up.
These are the HIGH DOLLAR BIRDS. Only about 8 (guess) known to exist. The run about 250K.
Dave Dare probably knows and can fill in the details.
"They were built in small numbers, to be replaced by the "Phase 2" with the bolt together case. There was a service bulletin published which detailed the replacement of the Phase 1 with the Phase 2, so the Phase 1 is extremely rare today. Parts for both are almost non-existent today. Paxton sold all their supercharger stuff to Paradise Wheels in California a few years ago.
The Phase 2 have a different boost relief actuator, housings that are bolted togther instead of the clamp of the Phase 1."
(Info from another Forum)
Here is a pic and story: