340 duster exhaust

I normally use Mr. Gaskets "Ultra Seals" but I didn't know they had that other one. Nice!

Deep throaty tone muffler? That would come from a chambered muffler.
Hooker Aero Chamber
Dyno Max turbo/Super Turbo
Summit turbo

Flow Masters do not flow as well.

Exhaust tune sizing should meet HP requirements of the engine and the cars performance needs. At 2-1/2 inch dual exhaust on the street (and sometimes strip) that would be very suitable to use.