flatter leafs flex better, but allow for more axle wrap.
and antiwrap bar is a great addition. unfortunately, if you can build a good bar, building a triangulated 4 link isnt a ton more work. why not build a bastard pack using your existing main leaf. i cant remember where it went, but along with the drive shaft pdf i told you about, i also used to have a pdf with various spring lengths and rates for all types of applications.
pirate4x4 may be your best answer.