I also have 275/60 on a 15x8 wheel on the back of my 68. I think it looks great and is the perfect tire/wheel size for the rear of my car. I like the 28" tall tire for highway cruising, but I need to re-gear my speedometer since it is reading alot slower speed than the car is actually traveling. There's some pics on the 68-69 pic thread (scroll all the way down the thread for all the pics) if you want to check it out:
http://forums.maxperformanceinc.com/...=639898&page=9