Well, I think you have a legitimate question. Those Magguts kits are kinda pricey, though.
Anyway, I think because of the cost, you just need to be careful to experiment with a kit for a magazine that functions exactly like the one you have. I guess you didn't remember that the Shield has what I think they called a "semi-staggered" magazine, so it is indeed wider than a single-stack, but narrower than a true double. I agree that the Kahr might be what you seek, but I'm not so sure if the baseplates are the same.