I've been using a two piece mount with 4 adjustment tabs that mate together. The outer ring is glued to the fuselage and the inner piece is bolted to the motor. The assembly is bolted together with 4-40 SH machine screws and blind nuts and installed and then when adjustments are needed I use shims on the tabs as needed to adjust up and down and left right thrust.
I've used it in the last 3 2m planes I've built including the Integral I'm flying now.

Attached is a very rough sketch.