Give a look to Classic Chambered Mufflers.
I am running the Cobra Mufflers ° No Glas Pack° on my FIA 289 N.A.F.
Engine 302
Flow core 2.5"
Muffler OD 3.5"
in/out 3.0"
Muffler length 28"
Verry happy and awesome sound from idling up to high revs and down shifting.
AC Cobra 289 NAF - YouTube