To The best of my Knowledge most companies that make 4 link or ladder bar brackets usually only make up to 3 1/8 tube radius or smaller so alot of grinding for very little advantage .
To Be frank i have done rearends for 25 years and have honestly seen more broken Dana 70s than 60s in the pickups they came in originally!
Usually the reason is that the inner pinion race spins in the housing and allows the pinion gear to deflect till they break
I Would just use a 60 and live a happy life without complications of the 70 Good Luck Matt