Whoa! Old Model Single-Six? Nope, ain't gonna work. The only "wide spur" hammers built during the Old Model days were for the large framed centerfires.
Of course, there's ALWAYS a way. I've purchased a New Model Bisley Single-Six hammer and cut off the upper portion and welded it to a OM Single-Six hammer's lower portion. One must NOT interfere with the hammer plunger spring assembly, though.