I don't remember ever reading about anyone doing a muffler mod on an 075 for milling. Its the saw I use and I don't think it really needs a muffler mod.
There is a guy over on the main chainsaw forum that did a full on port and polish on an 075. I think he even chainged the port timing as well as a muffler mod. You might do a search over there and have a look see at what he did and the results he achaieved.