I bolted a piece of aluminum angle to the prop head to check engine alignment. I measured to the vertical side seam near the seat back. If I had to do this again I would have checked alignment when I attached the engine MOUNT earlier in the project. In any event, the alignment was off a bit, so I used some washers and trimmed the rubber bushing a bit to compensate. Vertical alignment was also checked via a level on the prop hub and corrected slightly.