E3 vs.E9 exhaust differences
The pictures speak for themselves. However, although purists may scoff, where there is a will, there is a way. I have seen the E-3 center resonator/muffler and the secondary resonator (the bedwarmer) modified for use on an E-9. But you need to be handy with a torch. The E-3 rear muffler is too large to fit between the differential and the spare tire housing. So unless you want to take a sledge hammer to make it fit, it is hardly worth considering.
Years ago I had someone borrow an E-3 rear muffler from the garage so that he might measure it for use on an 2002. It was hardly practical because it hung too low and came awfully close to either the petrol tank and/or the spare wheel well, but I think he eventually used it. Interesting conversation piece, especially when driving over railroad tracks!
I cannot say for certain, but I have heard of others who used exhausts sections from Mercedes and possibly even Jaguar. The E-3 is a logical starting place, but one size does not always fit all.
HTH