muffler(s) on a Slant Six?

The first car I did I went Flowmaster 40 like most everyone else. The high speed drone was Loud. Couldn't hear the radio with rear shelf speakers at any volume. Now use Summit SUM-630125 Turbo muffler.Or Dynomax. Some guys do duals some single.I run 2 1/2 single to the back bumper. Just a thought..