Bronco Boy, if you're going for external hammers, under SASS rules, it looks like you are leaning towards the "Classic Cowboy" catagory

As mentioned, it ain't fast, but it is more authentic and it sure is fun.

Have a look at the SASS rules for the firearms and dress criteria and that may influence your final decision.
Many posses are just folks having fun and who don't want to get into IPSIC speed shooting, while some folks do both.
I've shot a Norinco external hammer coach gun for two years with no problems, after I filed and honed off the the sharp edges on the hammers.
Hammerless shotguns were originally allowed to be used, under SASS rules, because of the lack of external hammered shotguns that could be safely used.
The same thinking also allowed the 1897 pump actions to be used although they came in at the end of the era CAS portrays.
In any event, welcome to the sport.