Before you add a shim, you may want to block up the plane and set the 0 - 0 degree on the engine thrust centerline reference. After I set the plane to the 0 - 0 reference, I then measure the down thrust molded in the fuse. In my case, I have a digital level, so I can get to within 0.1 degree accuracy. I then use a draftsman right triangle and put one side on the vertical molded in nose area. I then put the level on the horizontal side of the right triangle. Then I add shims to the triangle to set the required down thrust. In my case the shim turned out to be around 1/16" thick. Good luck.

Steve