That's how I would do it, anyway. First, I'd get as much off on the Bench grinder wire wheel as I could, then dig in with the die grinder.

If I had to do it in the boat, I'd use the wire wheels on my drill. Drill is Bulkier to hold, so sometimes proper placement is an issue.

I'm assuming it is a stainless coupling, so I'd use a steel wheel. If it is not SS, you may want to use a brass wheel to not put the steel at issue of getting unbalanced, permanently.