I'd also go 3 inch if your headers are 3 inch, no benefit of necking them down. BTW I did the same thing on my F100 when it was a low HP 390 to prep for the 445 and it was a noticeable gain in the whole RPM range
2.5 mandrel bent will be fine, but if you are building an exhaust, intermediate and tail pipes do not change the torque of an engine if too large, but they can let it hang in a bit longer.
The reason I like the mufflers I listed is because they are absorption mufflers, they tend to bark wide open, but they don't bounce sound waves into each other changing them to mechanical and heat energy. The reflective mufflers do that and at some point have to resonate, every vehicle is different, but the FE strokers tend to drone where you don't want them to. Additionally, an absorption muffler tends to make more power
The Stainless Jones are a deal now and a real nice piece. Here is what I have, I forget the length I used, but I think 22
Here is mine, 3 inch mandrel bent, X-pipe, 445 idling
and just for reference, here is a set of Borla ProXS on my 489 Mustang with 3 inch exhaust and an H pipe. I really like the Borla, but they are 3 times more expensive for no benefit over the Jones. All the mufflers I listed in the title are about the same
Hope this helps
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 445 cid FE, headers, RPM intake, 1000 HP series Holley, 4 speed