I would take it off and I'm pretty good with tools and very mechanical. Have done a lot of work like that also. It's just I've learned when you only have one manifold, that's what you do. If you think you can hold a drill straight as a drill press, tap straight while leaning over, not drop anything down the hole.......do what Grigg says. Trying to advise with safety/risk vs reward in mind. (extra time to take off manifold vs better positioning of part, your body, tools. Thus avoiding a major malfunction). Considering an unknown experience level. Could be the wrong approach sometimes.
