I just put on a pretty quiet oval Walker with single exhaust on my 216. Now the lifters can be heard as the loudest thing, lol Like you I want the quiet so I'm also insulating the cab and inside the doors wherever possible just don't forget to allow the drain locations to do their job.

Larry
Old man᠁Old truck᠁neither one goes very fast. All you need in life is TIME, PATIENCE and MONEY.
If you are missing one component, you'll need an abundance of the others two.