On a 68 I run a 295 50/15....of course I have to have air shocks and if they blow the tires will just rub on the side wall and inner fender lip...I plan on getting stiffer springs though to compensate for this, Other questions on yours is there any modifications to the suspension system? Honestly tire companys make all sorts of low profile and wide tires, question is how much do you want to spend on tires? Not sure where you are, but in California for example, discount tire has a system that can tell them what fits some cars, and most tire shops at least from what I remember, used to be willing to order in a few different sizes and check it to the car by setting them up, some may not do this any more. It has been awhile since I purchased a set.