7 1/4?

A 7 1/4" with a Sure Grip and at least 3.55 gears will last a surprisingly long time behind a fairly mild 318. However, it WILL eventually break and the money spent to beef it up is wasted. For the cost of a Sure Grip and gears, plus setup, you would be money ahead to get a better rear in the first place. I personally do not like the 8 1/4" because it is a C clip rear and I have broken axles with a 4 cylinder Dakota. If I had a Dana 60 on hand, that is what I would use since having it narrowed to fit is way cheaper than buying an 8 3/4" that would fit.