Well Boosted, since you singled out the 66 Cuda as your car of choice, I think I can help...
The 66 has many unique, one year only body parts that should be in good condition on your car in question. They have a one year only front clip, rear bumper and lower body line that makes finding replacement parts much harder to find. True, there are some nice parts for sale on FABO right now for this particular year, but that is not usually the case. The front bumpers, grille, bezels and mounting supports are unique, the fender mounted turn signals are one year only, as is a bunch of the interior. The 66 Cuda dash is unique, and IMO the best looking cluster of any early A. All of the dash trim is unique as are the front bucket seat trim and back panels. Out back, taillights and the aforementioned bumper are unique as well!!
There are also some items from early A cars that are commonly hard to find. Things such as the drivers side underdash vent box with a good unbroken door hinge, front door armrest bases and pads, kick panels and other items are hard to find in any condition, although a few items are now being repopped.
Look for rust in the inner fender area, all the frame rails and rear spring perches, and other common areas such as lower rear qtrs, which are not currently being reproduced, and with limited demand, are not being saved by the 2nd hand crowd...aka...US!!!
All in all, the 66 is a great choice for a unique car that you won't often see, but again, I may be a little biased!! It seems to be the year I am most fond of for some reason!!! Good luck with your search!! Geof