I'll be shooting these to Doc in an Email in a few minutes... but if he can weld 6 brackets like this onto the rack (or something similar that he thinks would do the job) then this may be the best idea for a nice clean & custom rack setup.

For the model I used rough dimensions for the front-most mounts. Here, the center of the cross rails are roughly 52" apart. So with a 48" wide rack the bolt would be about 2" from the edge.

I'm happy I modeled this... with my custom stanchions the rack will be plenty supported. The middle and rear mounts will be almost completely supported on the stanchions as well since the rails taper as you get further back.