muffler(s) on a Slant Six?

I have a 2 1/2" flowmaster 40 (single exhaust) on my sl6, It droned pretty bad and sounded like a ricer with a fart can on it. I added a 2 1/2" X 24" glasspack to it in the back as a resonator and it mellowed it right out, now its has nice rumble to it.