Flat washers for 4-40 screws are close to 1/32" thick.

In theory, for one washer, the offset angle will be:

0.7 degrees if the distance between the center of the screws is 2-1/2"

0.8 degrees if the distance between the center of the screws is 2-1/4"

0.9 degrees if the distance between the center of the screws is 2"

Now, if your instructions give you the angles, you can measure them with an incidence meter or an aluminum angle bolted to the shaft of the engine.