Well Matt has explained the way it used to be done when no other options were available.

Three degrees right and three degrees down is a BUNCH, are you sure? Your concerns about stressing the mounting ears on the engine are valid and if it really does require that much offset, Truckracer has a pretty good idea.

As for setting or checking those angles myself, I use the electronic protractor from the Horizon incidence measuring kit and it's really easy. Just turn the fuselage on it's side for the right angle and leave it upright for the down angle. Compare the first former in the fuselage (F1 in full scale terms) to the prop flange and adjust as necessary.

http://www.horizonhobby.com/products...e-meter-HAN192