Still very much a "proof of concept" but I modified the pipes over the weekend just to prove I could get them to clear the frame and suspension. The photos you guy's supplied helped greatly.
I was able to modify what I already had in order to route the pipes to the rear of the vehicle and although I haven't included any mufflers I now have options to fit them, under the cab, under the bed and under the gas tank.
Fitting the 2 mufflers I do have onto the very end of the pipes there was no noticeable reduction in the noise output as a result of lengthening the pipes (though using a sound meter on my phone there seemed to be a slight reduction, maybe 2db, but Im really not sure how accurate that measurement is). However, as I said above I now have plenty options on where I can fit mufflers to try and cut the noise down a bit.
So I need to buy a few bends a couple of additional mufflers and maybe some additional pipe and a couple of days should see this done.