The uberti (cimarron) firing pin retaining pin hole in hammer is larger than a Colt and in the wrong (dimension wise) place than a Colt hammer.
You can make a cone shaped firing pin based on the cimarron (uberti) dimension if you have a lathe or you weld the tip of a uberti firing pin and reshape it ... you will have to open up the existing firing pin hole in the uberti frame a little.
I have done this on a ASM Hartford model to make it more authentic.. the ASM Hartford hammer firing pin retaining hole is different from a Colt as well.. so what I did was buy a Colt 1st gen hammer with a cone shaped firing pin in it and it was nearly a drop in fit... I can’t say a Colt 1st gen hammer will fit an uberti however.