I can't remember (or find) if I posted this but I called Tower, and there is a 'side note' that people seem to be overlooking that says that a muffler extension is recommended. I also called Hobbico and they verified that the 46AX probably wouldn't clear the cowl without an extension. Whew!

Thanks for the input on the silicone sealant and thread lock; I can't say I would have used either, but they both make so much sense.