I have a 6.5' bed. From the back of my cab to the closest face of the front cap is 44". Determining in advance what will hit first in an overtight turn with the bikes mounted is tricky, and depends on where the receiver is mounted, the design of the rack, size of the bikes, shape of the cab etc. I held the bike carrier up on the pin and guessed how it would turn out.
I put the receiver as far back on the pin box as I could while still having clearance between the front cap and the upright part of the bike carrier.
The 6" receiver I got from Harbor Freight. The angle irons were welded on by a local shop. I bolted it onto the top of the pin box.
A little dirty after a 6000 mile trip, but works great.