I have the feeling that 2.5 degrees will have you flying hands off large vertical circles. If a 35 to 40% plane is set up relatively well about 1/2 to 1 degree is generally all the engine thrust angle desired. Note I didn't say needed. Many like a zero thrust angle to make it easier to balance out thrust in both up and down directions, power on and power off.

Try shimming the mpotor mounts using pieces of 1/64th ply until you achieve the offset you like. Just drill a center hole in a few pieces and cut the hole up and through one side so all you need to do is loosen a bolt to insert or remove a thrust "washer".