Go to as many swap meets as you can and look for R/C guys selling off their Robart meters and get at least two or three. I also use some inexpensive common angle finders from Harbor Freight or the hardware store. A large flat area to work on, or I use one of those old Black and Decker small hobby vises to securely hold the airplane on a steady table. Move the airplane around until you are sure wings are level. Mount the engine in the airplane as you would to fly it. Attach one Robart meter to the crankshaft as you would a prop. The next Robart meter does on the wing. If you have a flat stab, you can take the meter off the aluminum bar if you have a third Robart meter and just set it on the stab, or use the angle finder at that point. Check all three at the same time and adjust as needed. I didn't go )-)-) on the last couple of airplanes I have been able to build. I subscribe to the Whitely theory of wing on the fuse center line, engine 1 degree down and 1 degree right thrust and stab at 1/2 to 1 degree positive incidence. You should do what you have success with. I need to go back and read Dave Trible's build thread and see what I can pick up there. This is probably the most critical part of the model assembly as far as simplifying the trimming of a new model once it's ready to fly. If things aren't straight and aligned, it gets more difficult.
Good luck and have fun,
Dan McEntee