The motor mount has the correct down thrust and right thrust angles for the PTS P-51.

You really do not want to change the thrust angles unless you have done something like screwing up a motor mount, so that the engine is slightly angled, etc.

Since most mounts are resin-plastic, I normally sand them down using a planar or band sander, to get any changes to the thrust I desire.

This works pretty well as the base of the mount is still entirely in contact with the firewall. It's also very easy and quick to do.