In the article Doug from Japan recently posted, a "BMEP Gauge" is
referenced, which is actually reading torque from the gearbox.

http://www.gami.com/articles/bttfpart1.php


Shouldn't it be pretty simple to make your own with a strain gauge and PSRU:

http://www.mistral-engines.com/var/ezwebin_site/storage/images/media/images/psru-open/1665-1-fre-FR/PSRU-open.jpg

In that picture, the stationary ring gear could be made free to rotate
against a strain gauge, which through some multiplier according to
gear ratio would give actual prop reaction torque, and with RPM known
power could be calculated just as easily. Do any EMSes do anything
like this this currently? As Doug's article points out, EGT is a
superior way to achieve best mixture, but a power gauge might be very
useful in its own ways.

-Chris