Nothing to add, really; some good advice up above. I did have a Mercury that was perticularly stubborn once, but it came off in the end. Heat may well have made things easier. I'd always tape those trigger pins up to stop them falling out. Scribe marks to help with re-alignment, yes, but you can easily kinda gauge it anyway. And I always clean those threads up once the gun is stripped and lightly grease upon re-build to assist future maintenance.

Hope all goes well.