This might be helpful, specs for the 53 truck:
http://chevy.oldcarmanualproject.com/chevyresto/53060.htmAs you can see the wheel is a bit forward in the rear fender. I don't think you want it any more forward than stock. The measurements might make sense and be helpful. You are correct about the perch and pinion angle, you need to have the frame loaded. Hopeful the picture will be helpful. Let us know how it goes.