The elimination tube is TTi's design. They just call them ""2.5" x 18.5" MUFFLER ELIMINATOR PIPES w/ ID SWAGE ENDS"". So the exhaust should bolt up just like their muffler was in place.

My current OE mufflers are 7" diameter and they have offset-inside/center 2-1/4" pipes with the stock R/T tips. I am using them as a reference and I have take dimensions from the center line of those mufflers to the frame and the tank. Referencing their online pictures for Ebody tail pipes (attached) and knowing that other members have welded in 4" diameter mufflers in the stock position, I am hoping to stuff as big of a muffler in there as possible both diameter and length. I think a 6" diameter will work but if not, then Magnaflow makes a 5" diameter too.
Once I have the TTi muffler elimination 2.5" exhaust in place (with the R/T tips installed), that should show me exactly the muffler space required. Then is it just calling up my local Oreillys and having them order me a set of that size.
If the noise is too much for my streeter, then that muffler elimination tube just might get a shorter 4" muffler mounted to it to help as a resonator.

Thanks for your reply.