triangulated 4 link on cast centre section axle. welded onto the tubes on each side. scroll down for the pic but also some info in there about others with the same kind of concerns as yours. remember to think about the different length of rods from bottom to top and how that will change the pinion angle as the axle moves up and down
http://67-72chevytrucks.com/vboard/s...d.php?t=261315
when cutting off old brackets or welding anything on the axle tubes ensure you take your time. the heat can distort/bend the axle tubes.