Use another source such as the machined surface on the front of cylinder head or the harmonic balancer or maybe the pan rail. They will all be 90# to the transmission output shaft. Remember the pinion will twist upward on acceleration so the static 3# will change a little. This isn't rocket science so unless you are trying to squeeze absolute precision like in a Bonneville racer a degree or so won't hurt your street rod. 0# will absolutely destroy the U-joints so shoot for the 3#.
The Jalopy Journal
