I have two questions.
1) If your Colt 1911 doesn't come with a beavertail, approx how much will it cost to get one installed?
2) Can you get after-market night sights for your Colt 1991?
Wilson has what you need/want and can do the work (along with about a dozen other 1911 specific companies).
My understanding is that it COULD need fitted, meaning polished and shaved to fit some of the grip safeties.