Get the centerline drawn on the aircraft as described above.

bubble-level the aircraft, on ts side with that line level.

you can now find the thrust offset with a 3rd grader's protractor and a foot of 1/32 music wire. pu a Z bend in the music wire... put the S bend in the pencil hole. Hold the protractor to the crankshaft and watch the wire swing to the angle mark. Turh the protractor around and do it again. (samd difference from 90? OK you got a good protractor. that difference from 90 is the angle.) If the wire is closer to the end of the protractor at the ngine.. the angle is up (whichever side of the plane is up)