If a guy really felt he needed a single trigger on his between-the-wars sidelock, wouldn't it be better to convert it to a double single trigger? The front trigger would fire both barrels, but, the asthetic among us would be pleased to find two triggers, the same age of the gun, still in place.
That brand new shiney trigger with the word "Miller" on it, hanging off a sublime English sidelock, seems about like candy pearlescent tangerine ghost flames, painted on a 1909 Rolls Royce. Very out of place.

Best,
Ted