I can't say about a Colt trigger guard and backstrap assembly, but there have been several custom grip designs that allow a Colt-type two piece installation. There is a strut added to the trigger guard assembly to support the mainspring.
As to the hole pattern, I've never tried to see if they are compatible. The Uberti Horseman revovler has a coil spring similar to the Ruger, and uses a strut which permits one-piece style grips to be used.
I believe Brownell's has a Ron Power grip for Rugers that utilizes a one-piece style grip.