If you're around Houston, Alan Horton does very good work on internals and such to make it a reliable shooter. And will do it at a reasonable price with fast turnaround.
Condition, clean it up with oil and brass wool.
Broken grip, don't replace it, the 4 notches that line up with the frame are an important part of its history.
With the serial number, you can look up the year of manufacture pretty easily online.
Frontier six-shooter = 44-40. For some insane reason, Colt didn't want to put 44 WCF on their pistols. I don't understand why, 32 WCF and 38 WCF didn't seem to bother them very much.