Here is the location of the cross member on my 68 short bed frame. Its just a touch over 5 1/2" from the rear of the frame. I drilled my rivet holes out to 7/16" so it could very well be dead on at 5 1/2". As far as buying a cross member, you have a couple of options. You can get them at ECE for 45-60 bucks with shipping. Or you could make your own. A piece of heavy angle iron or a piece of heavy walled square tube would work just the same. The easy and most convenient way to be to order one up, drill the holes to 7/16" and put some bolts in it.
