Sure grip 7 1/4 strenght?

I ran a 3.91 SG 7 1/4 rear in my drag car for many, many years. Just took it out last fall. Did not break it. The SG clutches finally started slipping. The weak part of the 7 1/4 is usually the spider gears. There are only two of them in a "open" rear, and the cone type SG. The Clutch type SG has 4 spider gears. IF the 7 1/4 was the clutch type SG I would not have a problem using it with an auto trans. I would not consider a 7 1/4 with a stick trans. Shocking the rear will kill it.

PS: Hypo65, You cannot put the wide ratio planitary gear set in a 65 down 904.
I'm not sure about a 66 or 67 trans, yes on a 68 up 904. I think on a 66 or 67, you need to change the output shaft also to use the wide ratio gears. That is why you can't do it on the 65 down, the later output shaft can't be installed in the early case. You will also need a fine spline converter to use the wide ration gear set. Then if you have a 64-67 273 the converter needs the small dia pilot to fit the crank.