I would not worry about having pin at axle center. I would start there, you can always move forward, when your limitations are more clear. GM standard beds have the longest axle to cab clearance.
I am 40"s pin center to cab, with no issues. It's like backing a TT, boat, snowmobile trailer, etc. You need to pay attention, be aware, or yes, any of these things will hit at some point.
You'll be able to back into most any site. Pulling forward at times, to lessen angle, then continue backing, works well for the tight spots.
Jerry
