Roland,
Just out of curiosity, is your Venus badly wrinkled?
I mounted my OS 55 sideways and used the Bisson muffler.
http://www3.towerhobbies.com/cgi-bin...?&I=LX8680&P=V
You will need to cut the crap out of your cowling. As I am sure you know, the Venus is designed to have the engine mounted inverted. I will post a pic, if I can find my wife's camera. I also have the same muffler on a OS 46 AX on my mustang. Both run just as good, if not better, than the stock muffler. One thing for sure, they SOUND a lot better than the stock muffler!
I didn't like the first few flights of my Venus. Just wasn't what I expected. But after playing around with different props, and understanding what the plane can do, I really like it. That pink bottom takes a little getting used to.[X(]
Keep the control throws per the plans. They don't look like much on the low throws, especially the elevator. But you will be surprised. The high throws are a blast. I have done half of a knife edge loop. Just don't have enough guts to try and bring it out the bottom. Some day though.