What is the widest wheel a 66 will take w/factory frame rails?

I am about to do a mini tub and a Martz 4 Link . Can I get 335/30/18 's in there like the camaros?
If not what is the max I can get in there with out removing the rails, I dont mind narrowing them. What are some popular sizes people use and backspace?


Sorry Newbie here doing a 66 , I will only ask questions once. Thanks in advance.

I have a 315/60/15 radial on a 10" wheel with 4"bs on my 67 and have notched my rails in half.