Kevin,

Paul had graciously supplied the attached pictures of just such an
arrangement [which I have attached.  I am just learning about all the
relevant considerations in aircraft design and operation, unlike so many
other people on this newsletter who are experienced aviators and
engineers, but to me a sprague clutch is most useful
if two engines are driving a common prop where it would function in an
"engine out" situation, or when starting.  To rely on a sprague clutch in a
trailing throttle situation might be tricky for reasons well described on
epi-eng's website here:
http://www.epi-eng.com/propeller_reduction_technology/sprag_clutch_misuse.htm
I remember there was some discussion a while back on how to counteract
trailing throttle gear chatter in Tracy's planetary gear PSRU, and the easy
answer seemed to be to simply maintain rpm above a certain level
[1800 rpm?] to keep the drive train loaded.

Your situation with your certified engine reminds me that certified engines
are certainly no panacea for minimizing headaches in aircraft propulsion
systems!

Paul has something pretty darn close to a firewall forward "package", just
by reading his website.  The advantage of his website is that it still allows
a considerable amount of customization, and allows people to start with
different engine year-models and rotor numbers [1, 2, 3 or more rotors].

Gene Kahn