Making a "test pipe", or as you call it a "muffler eliminator" is not
difficult. I looked into it then found a cheap new muffler I needed.
The exhaust system is put together w/ joints I will call "Stack
breaker" joints. This is so repair is easy and so the top section
can be pulled so truck heights can be lowered for transport.
There is an offset of 5" from top to bottom of these mufflers and it is
about 32.75" end to end. I found what I believe are the same
ends used, male and female
HERE. I am sure if a guy looked he could
find 2- 4" exhaust pipe 45's and make a section w/ a 5" offset and
32.75" long, w/ a 9" straight section on the bottom quite easily.
The pipe TMustang buit will probably start to break and fail
just BELOW the Ubolt we see. It really needs to be strapped up
top as well IMO.
So a muffler can be eliminated and the muffler guard be reinstalled to
keep the OE look if you please. There will not be a huge difference in
how loud it is. It will be noticeably pulling hills.