FWIW, a 9" owns a rear D60.....just as strong, better clearance, lighter weight. if he upgrades to a 35-spline 9" like i said (big bearing nodular 3rd, Detroit/ARB/spool, 35-spline shafts), he can run up to 44s without any issues if he drives smart.
for the front, either a D60 or, for...