When I got my truck the previous owner had swapped in a W56B and used u-bolts to mount the cross member. The bolts do not need to be welded to the frame if you don't want to. The bolts on my truck were not and it made it easier to R&R the cross member when needed.
I actually have a recent picture of this, hang on a second...
Ok here we go:
I did this back in Spring '08 to get me around town for a few days while I was in between Rock Crawling (low profile) cross members. The u-bolts shown are our regular leaf spring u-bolts, which are the wrong size, so I built those silly plates to pinch the cross member in place.
The proper method to do this would be to measure the bolt pattern of your cross member and use that to source the correct u-bolts. They should fit pretty snug around the frame. Then trim excess length of each bolt to minimize the possibility of damaging the threads over some rocks.
BigMike
Thanks Mike, couldn't find my old pics. I did weld mine in just because. Don't forget to trim them.