Shackle Position

I was at a car show a couple of weeks ago and was looking
at a 70 Duster that had been tubbed and the springs were moved
under the frame rails. I noticed the rear frame rails were notched.
The rear shackles were at about a 4'oclock position not straight up
and down. I had never seen this before.I was just wondering if this
is the proper position? With the rear shackle in that postion,would
this affect the way the suspension would work?I am going to assume
he had super stock springs and the frames were tied with a 6 pt cage.
I did not get a chance to talk to the owner.It was a real nice car.