Following up,
I agree with everyone that extending to the back is the best solution. Having too many projects on the go this summer I decided to go with the quickest, option 2 above, making a silencer to stuff in the tail pipe.
I'm quite pleased with how much difference it made, the brain pounding drone is gone and the truck is quieter overall. Any immediate need to spend a weekend fitting chunks of U bend up over and around rear axle, trailing arms and sway bar is gone! No apparent loss of power and the engine still has some rumble
Here it is, not really finished yet as it is just tacked together so I could drive to work with it bailing wired in and see if it was worth more effort. I'll finish weld it, trim it to be hidden in tailpipe and bolt it in.
