I think I had found that with a 17" wheel you ended up with nearest to stock tire height with the 255/50/17. the only problem is that you are right, very hard to find. I very seriously thought about buying GoodYear Wrangler F1's for my car wehn I got my current tires and wheels. This is their max performance truck tire and it came in sizes I liked better than car tires did. I was really hung up on having Wrangler on the side of the tires on my car though since everyone knows that is the truck tire name so I didn't do it. It doesn't seem like a bad idea to me though if you can get the size you like in a nice tire. I ended up going with the 18's in the back just to get the tire height right. I have 4.10's and have a pretty accurate speedo that way, you see guys running short rear tires and 3.73's that want 22 tooth speedo gears, my combo calculates to needing a 21.4, making the 21 the best one.
Former owner of 94 Bird with DOHC 4.6L swapped from a mark VIII
2011 CTS-V Wagon
1968 Torino was an original 289, C4, fully documented numbers matching car. Now: DOHC 4.6L/T-56 swapped, Cobra intake, IMRC delete, BBK long tubes and H pipe. Dynotech Aluminum Driveshaft, 9" rear with TrueTrac and 4.11's.