Some models have zero right and zero down. Others may have three or more degrees. I do not know what is common for powered gliders.

Will you be using a cowl, or will the engine (or motor) be open?
If it's open, you can do this the easy way. Just use washers or other shims behind the mount to adjust the angle until it flies the way you like.

If using a cowl it's harder because you need the prop shaft to be in a certain spot.