I finally got around purchasing the 2.5" TTi X-pipe and tail pipes for my Challenger. I then decided on the Hooker Max Flow mufflers. I have read many threads on these mufflers and they all suggest that they are LOUD at WOT. Some of the tests show that they flow 521cfm each and the decibal reading at WOT is 120+, which is the same as a 2.5" straight pipe. Due to this, I wanted to add resonators beside the tank to try an lower the WOT sound a bit but I want to keep the exhaust as straight through as possible for a street car. I do not want to attract the wrong kind of attention and I do not want to wake up my neighbors, so a resonator is a must.

Mounting Resonators to the TTi Challenger tail pipes:

TTi told me that they do not make their tail pipes for resonators, but with the help of Eric from Classic Chambered Exhaust, he has helped me come up with a resonator that will fit onto the TTi tail pipes.
Most of the aftermarket resonators that I looked at had 2.5" ID bushings on both ends which will allow them to slide onto the outside of a 2.5" pipe. But, since there is only about 16-18" between the centerline of the muffler mounting bracket and forward before the tail pipe makes the upward bend to the axle, I needed a resonator that has a front bushing with 2.5" OD to allow the Accurate R/T exhaust tip to fit in this area. So Eric made me a set of resonators that have the 2.5" ID bushing on the entrance side to allow the resonator to slip over the TTi tail pipe, and he has added a 2.5" OD bushing on the exit end of the resonator to allow the Accurate R/T tip to slip over the end of the resonator. Mounting the exhaust tip onto the end of the resonator makes the assembly shorter and easier to fit into this area beside the gas tank. The resonator that Eric made is #25-RES-SPE. It is a 2.5" through pipe with a 4" OD x 12" body size. The bushings extend beyond the case by 2.5" per end. This is the first "off-the-shelf resonator" that I have found that will fit into this area for my 70 Challengers with R/T tips and TTi tail pipes.
I could not have STUFFED a longer resonator into this area! But this combination fit perfectly into the area beside the Challenger gas tank. There is plenty of room to go larger on the diameter of the resonator in this area, but no more room on the length.
Thanks to Eric at Classic Chambered Exhaust! Excellent customer service!!