Scott,

The 337 form can be sent in before the work begins. This allows for
approval/disapproval before a saw is taken to the airplane. I imagine
you will have to hire a DER (designated engineering representative) to
do an engineering analysis to accompany the 337. Harold Kasola is
very easy to work with and has Kasola Engineering in Albany, GA. A
call to him would be worth the effort. Having just certified a club
glider in experimental (last week), I can tell you it took a few days
and a trip to the FSDO.