I messed around with this for a while. Ripped the frame up a couple of times. The conclusion I came to was that you need a crossmember right where the front hangers are, and at very minimum boxing from that crossmember to the shackle hanger in the rear. When I changed my springs so that they were just barely outside the frame it made a big difference in the way the truck drove. I have pretty soft old springs on, with the springs under the frame the truck dang near flopped over on itself on pavement. When I put them outside the frame it helped this alot. Also I did not lose any articulation from putting the springs just outside the frame. I think that the springs can only twist so far and then they don't go any further.
