Moser makes 28 spline c-clip axles that fit as replacements. I've had them for four years. The fitment problems are with the 26 spline carriers that won't allow the 28's to enter at the carrier bearing diameter. With a 28 spline designed carrier the axle doesn't need to neck down to pass through. Don't forget that the stock cast carrier is sorta' weak also. I'm in the high 11's.
i say you should put better axles in it and c clip eliminators if you plan to race the car at all. not much fun chasing your tire and axle down the track after it comes out of the car when it breaks! i know...i did it!!
I guy I know has been 7.30s in the 1/8 mile in a street car and never had any problems I think the car was a foot brake.
I broke 8 or 9 in one summer with a 4 speed most of them on the street I think my car ran in the high 7s at the time.