If you aren't planning on running longer shackles, you shouldn't need to worry about welding in a x-section. The stock length shouldn't twist much if at all. You should be able to just run 2 pieces of 1.5"x 1/4" flat stock at the length and just drill holes in each end.

This is a welded set-up I did for my flatbed rig. The shackles are 3" longer than stock which yields 1.5" of lift. If you don't have access to a welder, you can bolt a center piece in and get the same result as welding.

If you have to get new spring bushings you will have to fab your own. I used some CJ bushings that I had to mill down using a grinder to get them to fit.