This is one of the photos from the photo album mentioned above.




As you can see, you don't need much at the base of the mast. If you want to go to the trouble of running an internal downhaul you can simplify the look of it even more.

In answer to the rules questions, you can do what you like for a downhaul or rotation control.

I can't emphasize strongly enough that everyone with a Mosquito should read the rules. They are not very long or hard to read, and a lot of wasted effort can be saved by checking first what can and cannot be done.

The National Mosquito association web site has the rules in PDF form to be downloaded.

Mosquito Building rules and regulations