You are right about the welding Yetibone; youll have to do it rather slowly, proceeding only in short strips, and dont cool it with water afterwards - it will harden the seam.
I have seen similar aftermarket trailing arms like those Superman, but again: I`m on a tight budget.
This is something I´m looking after:
http://www.fordmuscle.com/archives/2001/03/controlarms/
Justin