The only clips I can really find are of them on Mustangs, unfortunately.
The magnaflow is highly recommended due to it'* price, and the fact that it'* also a crossflow muffler. A.K.A. a Camaro/Firebird muffler. And almost everyone else seems to have one.
I didn't go with one because I didn't want mine to sound like everyone else'*, lol. No offense...
For example, I'm using a Cherrybomb Vortex muffler.
Most mufflers will be anywhere from 13" - 18", with 4x9" - 5 x8". Here'* an example, using a Flowmaster. They're dimensions are 13" long case, 19" overall length, with a thickness/width of 4x9.75"
That'* about the most common size you can go with, and almost every muffler company makes them that size. The case length you'd prolly want would be from 13" - 15".