The right thrust should already be built-in. Don't add any extra angle, just mount the engine so that it is straight on the mount. It may look like it points a little to the right, as viewed from the rear, but that is the right thrust already built in. When it comes to where to mount it fore and aft, just make sure you mount it enough away from the firewall to make room for the fuel lines coming out behind the engine. None of the thrust angles are too critical on a trainer unless you can't get it trimmed properly in the air. Even then, a ARF that is difficult to trim usually has a problem relating to how well it was built, especially the tail feathers. Make sure the wing and tail surfaces are square and true to the fuse and you will have no problems.

Jesse