Earlier, Willie wrote:

Regarding your engine options, It would certainly appeal
to me more with a four stroke, than one of the Rotax's
mentioned on the site.

We've (Brad and I) recently gotten a couple of messages to that effect.
We'll keep it in mind, but it's pretty important to keep the engine
installation weight as low as practical in order to get decent sink
rate and soaring performance from our basic 108 ft^2 15m wing.

Thanks, Bob K.