Re: New to the board, new mb owner, modifications
Welcome to the forum. I think you'll be very pleased with the 54T and it should carry you up those hills with no problem. My first bike was set up with a 44T and here in hilly Colorado it pulled my skinny butt up every hill I encountered. You're like me being unconcerned with top end speed but you might also consider a 48T. It could be a good compromise between that hill busting 54 and your current 44.
As for the muffler, some guys have had good luck using course steel wool or fiberglass as a sound deadner. Goes without saying that you'll need to fabricate some kind of cannister, maybe your old cat will work, using a thru pipe, drilled then wrapped with the material and a tail pipe of sorts. Good luck.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"