In order of loudness (and legality)

Turbo Type mufflers (the larger the core diameter the louder they are, I personally prefer a 2 1/2 in core )

Glasspacks (yeah I know there are more efficient mufflers)

Burned out glasspacks (the straight through type instead if the type with the seperate inlet and oputlet cores)

Straight pipes.

My personal favorites on old hot rods are the burned out glasspacks or straight pipes (full legnth 2"-2 1/4" .pipes) nothing soumds more period correct if you can stand the noise.

If you can find them the old can type Thrust mufflers or smittys aren't bad either.