OK I see...if it a had a standard roof it would be a Coupe DeVille, but as a convertible it's considered a DeVille Convertible.
Yeah... Coupe and Sedan DeVilles were both "Hardtops"... no B or C pillars. The Fleetwoods and Limos were stretched "sedans" with B and B&C pillars respectively. Convertibles were the DeVilles and also ElDorados. Not many "econo" Calais were ever seen... which kinda laughingly might make them even more valuable.
OK Tony a trip down memory lane....upon opening the hood, what unusual feature would be CLOSEST to you?
Not sure what you mean by "unusual" and/or "feature"... and if the unusual feature was as compared to Cadillacs, or to other cars?
But... if I remember correctly... the Battery was up in the Left-Front... with lots of AIR between the grille and the radiator.
Here's a photo... expand it and see the battery, horns, dryer and the ground! I think the battery being up front like that was the only "unusual" thing... and possibly a "feature" so that it could be easily jump-started. OH... and the Battery had a "Delco-Eye"... which is the second cap from the right on the battery. It enabled one to SEE the electrolyte level without removing the cap. It was a "good" indication, but not the BEST idea. Some of the other cells could be low and you wouldn't know.
Other stuff might be:
I believe the '66 was the first year of the 429 with the 3 speed Turbo Hydromatic... but everything else with the exception of the 3rd member in the rear axle was about the same as many years prior.
The 3rd member had NO bolted on caps, but the casting was cut diagonally where the caps would have been. Somehow the factory took the ring and spider gear assembly and walked it in at an angle and then pressed it into the "caps". WEIRD... and unrepairable!
Hints are available for $20 apiece.
Of course if you have the right answer, ALL of your $20 debts (and you got alotta them) are wiped clean!