On all three accounts. Lighter is better, everything sticks out of an ultimate cowl, and Stan's does make a nicer one that is a little bigger.

The head will stick out the side of the cowl as well. Make sure you've got some room around the engine and muffler for vibration and air flow.

You know, that 91FS will do really well on a 60 size aerobat!

If I can find the pictures of my old Ultimate I'll post them. I think there is a shot that shows how the engine fits in the cowl.

Happy building,

Scott H.