The tower muffler can be purchased from Tower Hobbies for $14.99 mail order. RCU has a search engine directly to Tower. It resembles a Nelson pipe, but about 1/4th the price and about half the weight of the stock muffler. It is the standard muffler for the Tower Engine. It fits OS, Magnum, Thunder Tiger engines. Most engines will pick up between 900-1300 rpm's increase on the top end with this muffler over stock. You will need to re-needle after putting one on, because they have better flow than the stock mufflers. Throughout San Antonio, you hardly see anyone using stock mufflers on .46's and .50's anymore, due to the increased performance you gain from these things.

Good luck with your project.