Cody,
I feel your pain. I had the same problem. I was lucky in that a member on another forum had a sight that was .385" wide. I have no idea where he got the sight - it was laying in his parts drawer.
The problem with the oversize sight pictured is that although the dovetail measures .465", it's also .125" thick. The dovetail depth on Kibler's SMR is .050". By the time you reduce the thickness of the base by .075", the base width may be too small for the .390" dovetail width. For $10, I'd get the sight and see if you could make it work. Take the oversize sight and rub it back and forth on a piece of sandpaper on a flat surface. Keep measuring the width of the base until you get close and then try fitting it a little at a time.
Good luck,
Kevin