Hess and Eisenharts were made in 87 and 88. They made approximately 2000 cars. The H and E specific parts are hard to get.They used 2 fuel tanks, 2 weird senders, and the rear window motors . The top stacks flush with the body when down. These cars were troublesome when new, but most survivors have been sorted out.
Factory converts started in the 89 model year. I like the 89s the best. No air bag, a one year only steering wheel, early cars have lucas ignition and distributor. The wood was "bookmatched"and the door wood have inlays. As the cars get newer, the doors lose the inlays, etc. In 94 thru 96 there was a 6.0 litre V12 available, with the 4 speed auto. Very low production, and a really quick car.
The 4.0 litre cars are simpler, and take less maintainence. They are not as cool though. Nothing beats a V12.In 94 there were a small number of 5 speed cars sold here. Rare and nice.
In short, in my opinion anyway, the newer they get, the cheaper they get. Ford introduced some cost cutting, and if you see enough cars, it shows. If you find one that you like, then it doesen't matter. Just drive and enjoy.