If you are proficient with a tap, I think that is a good and simple solution.
If you are not, it is not that hard to learn. Go slower than you think you should. Back the tap out frequently, and use some sort of oil. And do not do it in the cold (a reminder I could have used a couple of days ago when I snapped off a cold -and therefore more brittle- tap).
Tapping pressed steel is a snap. Aluminum is pie. Surely the RD body is one or the other.
let us know how this works. I think your idea to use longer limit screws to reduce the range of the RD is a clever one.
jim