3/4 frames...

okay stand your 2x3 up not on its side.how thick is the 2x3 remeber the actual frame is not that thick and is very strong.if you make it stiff and rigidit will brake .look again at yourold frameit is not that thick and it pretty strong there are only 6 crossmemebers.i think you are on the right track just a little fine tuning for your exhaust and it will be one badass frame. and where you want to start your frame is 6 to 7 inches after your upper control arm but that is my 2 cents

as said before, it would be true minitrucker (not in a good way) to run the tubing on its side like that. i like the ladder/perimeter frame hybrid tho - but also someone mentioned exhaust. where are you going to put it? can't run it under the frame. it's deffinately going to have to be fully custom.
you could run some 2x4 .120 wall tubing, on end. that would be plenty strong, narrow like you want and have some round tubing as the outer perimeter frame with your body mounts there, a well placed gusset or two here and there... viola. check and make sure you won't hit the tranny with that narrow of a frame.
i don't know if i'd run the bags and cantilever on the 2x3 on its side tho. especially that far up on the bar. something is going to bend.