What Beam said.
Rule of thumb is roughly 1hp per meter. Tohatsu 5hp 2-stroke would be a good call too. You basically want something with a narrow engine cowl. When main engine is on hard lock there"s no contact with auxilliary. Look at long shaft too.
Also consider some sort of anchor point to ratchet the auxilliary in the tilted position, as the tilt locks on these smaller outboards wont stand up to the vibration when underway.