The easiest way i know to add right thrust after the plane is built. is to use Earnst thrust plates. they come in 20-40 and 60 size. use the one that works with your motor mount. I have used washers in the past to experiment. Problem with the washers is the dig into the firewall after awhile so your right thrust becomes less than where you started. Try the earnst they come in one package with 1,2 and 3 degree shims for under 3.00 dollars.

Dennis