Serious question, why not try the drop in magwell conversion for the .45 grip to 9mm?
Two reasons, both to do with the magazines:
1- Uzi mags are cheap, available, reliable, robust, and I have other guns that use them.
2- A reasonable supply of M10/9 mags (say 10) cost as much or more than the conversion did. I don't have anything else that uses M10/9 mags and therefore don't already have them on hand. On the other hand I have a good pile of Uzi mags.
The Uzi grip is also more comfortable IMO than either of the stock M10 grips. YMMV on that.
The M10/Grease Gun mag grip is much better for shooting .45 ACP than Uzi mags. Perhaps I would have tried the adapter and M10/9 mags if that had been a concern. However, with two M10s I decided the best route was one with a Uzi grip for 9mm and one with a M3 grip for .45 ACP.