When you say early, what is the serial number? Lefever Arms was notorious for not building guns in numerical sequence; so finding low serial numbers with later features and vice versa is not uncommon. I suggest you post additional pics to help make a period determination (be sure to show the cocking mechanism); but to answer your question, I'm sure Lefever would have installed a single trigger in an earlier gun on customer request, as it seems there was little that company couldn't do in the way of custom work.
