Frimath,
I, for one, would be very reluctant to modify a USFA with any parts that came from anywhere other than the USFA factory, assuming that your "lightning grips" would be of Italian (Uberti) manufacture. It would completely destroy any collector value that your gun would hold (and lets face it, USFA collectors and SAA purists are where the money is at these days).
There were no "1877 lightning style" gripped Colt SAA's back in Doc Holliday's day (or, for that matter, even our days) so why try to replicate something that never existed?
Shoot it, enjoy it, keep it, but don't modify it.
CJF