You actually don't need a different housing for additional tire clearance. Where the axle ends are is not the limiting factor as the first interference point is the leaf spring. Moving the springs in an inch removes the interference.

If you move the springs in then you can either A)bolt in a B body rear or B) keep your E body housing and weld on new spring mounts to realign with the the new spring location. Bolting in a a B housing simply eliminates any cutting or welding. It doesn't actually create any additional room over using the E body housing.

Of course, different offset rims are required if you use the E housing compared to the B housing if you are going to maximize the new space from moving the leafs.

If you do go the B body route, there is a difference in width between 67 and older and 68-70 that will impact you rim offset selection as well.