Ok, so I found how to measure the bed. 53 1/2 inches from the cab is where the hitch should be centered. It should result in it being just forward of the axle a little.
So my next next question is on the setup. The rails run the length of the bed not across and bolt into the bed. Under the bed there are thick square washers to secure it. He did not have any connection bracket to the frame and said that's the way the rv dealership did it 3 years ago. My question is, is that throng enough for the hitch? He has towed it without issues and was installed by supposed experts so I'm guessing it's ok. Tho where safety is concerned I don't like assuming. Any advice or opinions?