I've just builded an Carl Goldberg's Extra 300 with a .91 FX OS Engine. For the covering and finishing touches I send it to a friend who owns a hobby store and he changed the position of the engine mount so NO right thrust is included. I asked him about this and he told me that there would be no problem and that he mostly builds without any right thrust almost all planes. Tha plans ask for 2 degrees of right thrust and he changed the position of the mount so the fiberglass cowling could fit straight and looked OK. Has anyone flyed this plane with the engine mount exactly in the middle instead of a little to the left and without adding the washers to make the right thrust and consequently align the engine to the center?
My friend says he has flown several planes without adding right thrust and that there is no difference.
Should I only need to apply more right rudder on take off? What is the real reason for the 2 degrees of right thrust?
If I do need the right thrust I will have to make several changes (adding new holes to firewall, adding washers and changing the cowling position).
What differences in flight should I expect with a plane without right thrust?
Thanks

You will need the right thrust if you want it to fly true. Yes, you can trim it out with rudder but that rudder trim will always be there, adding drag, and will effect roll coupling a little,.....this will need to be trimmed but may also effect elevator.......
Unless you are a pattern flyer you probably won't know much of a difference. Some people don't even know the rudder exists.
On the other hand, if you are serious about making it fly as straight and neutral as possible stick a few washers under there. I did. Really good trimming is an absolute science. It can reach the PHD level quickly for a pattern pilot!