Axle Swaps

R&P makes them to order. They have the plate blanks in stock then weld together according to the customers needs. Just need to let them know what axle you're using, and where the shock mounts need to be. Whether you want them to be slider style or standard style, etc.They do double shock mounts too and can supply u-bolts as well. I'll agree though, most "mainstream" or mail/web order places don't stock them for the older axles or even realize there is a difference.
Of course for a guy with your skills a couple of spring plates are nothing to fab up!