building 273..or not

I plan on rebuilding the 904 and upgrading to a 8 3/4 with 3.91 gears ...any can suggestions? ??not sure if I should go. 30 over or stay stock any input

I have the same thoughts, the problem is to find a 8 3 / 4 rear axle with sbp, SureGrip and 3.23 ratio.