Nylon Screws: NO WAY! Replace with Metric metal screws, or better yet, glue the booms on. I will do that on the next one. You can still unscrew the stabilizer if you have to take it apart, but so far, I've not taken my wings off for any reason.

Exhaust: Get a Jett Pipe - tell Dub that you're using it on a Bobcat, and he'll modify it for you to send the exhaust out the back. I posted a picture of it previously - don't ask where, cause I don't remember...but it's somewhere buried in this thread. Put it on the OS 55 AX and you'll be VERY happy. My Bobcat (with the pipe and 30% heli fuel, APC 11x7) was clocked at 133.8 mph a few weeks ago. (I also tried the Weston pipe, and I do not think it perfomed as well, but plugs and fuel make a difference, but after flying with the Jett pipe, I had no desire to experiment. My Weston pipe (1 flight on it) is for sale: $50 + $7s&h if you'd like it).

TOWER 75: The Tower 75 probably does not generate too much more power than the 55AX, and it doesn't want to turn as high an RPM, and it's heavier. Yes, it's $70 less, but IMHO it's not a good buy. You will need to add weight to the front of your plane to make it balance, and I truly do not believe it will go any faster at the end of the day, and you've raised your wing loading for no good reason.

Bottom line: you get what you pay for. I've heard a lot of good and bad on the Tower motor. I've only heard good about the OS 55. PS. I just bought the Cessna 310 Twin from Top Flite, and purchased 2 more OS 55 AX's for it. I would not trust my $1800 investment to a "cheap" motor just to save a few bucks. This is only my opinion, and we're all entitled to one, right?

Good luck!
Mark