If vibration is caused from too sharp a driveshaft angle, why not use axle shims? I've seen them in 4 to 16 degree incements. they go between the axle and the spring, to tilt the axle to a less offensive angle, and prevent the vibration problem.
Of course I have no idea if they are still available, as this was 15 years ago. <img src="/forums/images/graemlins/zombie.gif" alt="" />

1994 Chev S10 Ext.Cab with C223 5spd
1991 S10 Sonoma Ext.Cab with C223 5spd - SOLD

Kubota B6100 diesel with accessories