here's my .015 cents, if you're going to all the trouble of a one off 3/4 back frame, why not go the extra 1/4 and built a complete one off frame? And if you want to keep it lighter could always run round tubing..
round tubing is for the pro's only..much harder to work with and if your welds arnt perfect forget about it the thing with snap like a twig.. you would have to build the frame like a "ladder" and mucho triangulation..
Tis is true... i just dont wanna see the kid get in over his head...to be totaly honest..if ya just did a trad bd. with a 2x3 backhalf you can have your truck back on the road in a week or so can still run narrowed rails.and it will still look awsome.