My planes are either scratch built or built from kits, some call for thrust and some don't. I start out with zero thrust and fly the plane to see if it needs it?? I will use washers out at the field as/if needed until I get the plane into trim, I have several planes with zero engine thrust and don't require it. When I get home I measure the washer thickness and make up a tapered hard wood or ply spacer and replace the washers with it. If you don't all the forces and vibration are on that small washer area instead of the complete mount/fire wall. If two degrees are called for on a plane I measure from the fire wall to the front of the thrust washer of the engine, say it's 6 inches. On a sheet of paper I draw one straight line 6 inches long, I then measure 2 degrees from the top of that line and mark it along the side of the first line with a small dot. You can buy rulers with degrees or round degree meters, just draw a line from the bottom of the first line up to the dot then measure the distance between the two lines. This gives you how much off set or how far to the left you have to mount your engine to get the prop to be in the center of a cowl or just be centered in the plane. I'm sure Ken or someone has a drawing of what I just tried to tell you, a picture and that thousand words thing.