does my frame look shortened?

[1970 C10 MJW]

hey guys I am working on my truck... and I have never had a correct rear bumper on my truck, someone custom made one (2 fence posts welded together with some flimsy brackets), so I ordered the rear bumper and bracket and i am looking at the rear of the frame and I cant find any bolt holes that line up for my brackets... the very back of the frame is the only place where it could have been shortened considering its a long bed and all the holes line up for that... any ways i cant figure it out.. any help or pictures of the rear frame section with bumper/brackets would be awesome! the exhaust/ tips have been on the truck for a couple years, and the ended at the end of the old bumper, the old bumper had probably only and inch or so of a gap between the bed