Glad you fixed it.
I'm pretty sure the M110 is an interference engine, so you'd need to unbolt the cams to prevent valve contact while rotating the crank with the chain detached.
I did the chain tensioner on the M104, and I finally had success levering the cap on using a screwdriver as a pry bar and then turning with my other hand. It was still a bear and required multiple attempts.

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Prost!