Hi! I recommend you to use washers on the left side of the mount. And if you wanna be really cool you first put some washers on the upper mounts. This is for some down-thrust. It's a fact that any airplane, high or low winged, WILL pull the nose utt on accelation or down on decelleration. To prevent this you can put washers on the top mounts to tilt the engine a little down. 1 or 2 degrees often helps alot to keep the plane pretty level when throttling. When it comes to sideways thrust the easiest way to measure it is by just trying for example 2 fairly standard washers on the left side and just test taxiing the machine. If it tracks ok without suddenly pulling to one side during throttling(without paying attention to eventual toe-in or out on the gear) then I would test flying the thing.

There's surely a thousand ways of doing this, but this is how I manage.
Good luck!