All excellent questions George posed which need to be evaluated. Vredestein, Dunlop and Pirelli are all excellent choices and stick like glue if you enjoy spirited corners - I've used them all. The Dunlops probably only yielded about 20K, but were fun to drive. These were all on stock rims of the 1972 1800E.
In '98, I mounted a set of Dayton 72 spoke wires to keep the period look. Dayton did not have rims to fit the later model 1800s, so they custom made a set for me to my specs. The only thing I remember about the size was that I went about 1/2" oversize in width, but I don't remember if I compensated with offset. The tire size I chose was 195/65 R15 because I was trying to maintain overall tire circumference as close to stock as possible. Using a 195 tire width did cause them to rub at full turn in the front, which I solved by spacing the front 1/4" each side. This increased front track by 1/2" and considerably improved handling, especially in corners. The narrower rear end seems to tuck-in nicely. The tires I used were Viper directional radials, and have been very pleased with them. I'm not sure if these are even available anymore, but I am sure there are many other brands that exceed the performance of the Vipers.
One thing I need to mention is that if you do not have IPD's anti-sway bars installed (front AND rear) you should seriously consider doing so. Case in point; under hard cornering with the 1800s, the inside rear wheel has a tendency to lift off the ground and by "off the ground", I mean by several inches! Unless you have someone following you observing, you might never know it. Needless to say, this probably doesn't help much in keeping control of the vehicle. With the anti-sway bars installed, no problem.
There is nothing eye opening with this set-up but, "Oh man, what a difference in handling"!
Keep us posted on what you do as this thread will be of interest to many.
I want to die like my Grandfather did, peacefully in his sleep.
Not screaming in terror like the passengers in his car.