DocMan- I run Colt mags on a Mil-Spec lower but the lower was cut for 9mm from the get go so the block wasn't needed and after doing a vast a mount of research on magwells came up with a big goose egg. I think your problem may be worse due to the standard receiver and then due to the block going to 9mm. I ended up getting in contact with Bob Novak over at Techwell and he built one for the Mil-Spec. Its on their website under the CMMG label and it turned out perfect. FWIW Bob was great to work with.
Another option, plus probably quicker and guaranteed a hell of a lot less frustrating, is SMF Tactical has dedicated 9mm Colt lowers and purchase the magwell. Just my 2 cents.