You do not need to tack the spring hanger. What I did was mount the axle and springs with the shackles and the hanger. Then I put the hanger where I though it should be and used "C" clamps to hold it in place. I started out with it flush. Took it off the jack stands and put in on all fours. Seen if I like the shackle angle. If I was happy with it (which I was) I made sure it was centered and tack it up.
I do not know if they are still the same way but A-P's hanger used to be made to be mounted in two different positions, one way was for stock length 79-85 springs and if you flipped it around it was for their longer springs. This is the way it was when I did my SAS in 1999, I do not know if they are still made that way.
