There are a few companies that make the Johnny Joint stuff, plus I think there are some you can use in the stick arms. I'd definitely box the lowers if I ran stock arms though.
As for the del-alum... I think I'd stay away from them in the back. The whole damned system is made to bind, relying on the stretchability of the stock rubber to alow the arms to grow, shrink, or twist. Anything that stops this action causes bind, but the Johnny Joints seem to be OK per the testing of a few on this board.
Shiny Side Up!
Bill
'72 442 "Inamorata"
http://www.fquick.com/ProTouring442