"There are no shifter bosses brazed on to the down-tube (although there is the ubiquitous pip to prevent clamp-on shifters from sliding down the tube). "
Some believe shifting is crisper with clampon instead of brazeon lever bosses. Eddy Merckx still makes some KOF steel frames this way. In one description of a model it states that this was indeed Merckx's belief. I can't offer an explanation nor claim that I really would notice the difference. I always assumed that the primary reasons for having braze-on lever bosses were just matters of convenience, appearance, and no paint scratch worries.
BTW why don't we still see those rubber or plastic lever covers anymore. I liked the padding!
Some of my friends at work (then all lab method development food microbiologists in their 30's to 40's) formed some buying group (late 70's to 1980 or so)to buy a bunch of Mercian frames direct from Derby. They all had their own ideas for building these up in their own way.
It was from them I first learned about campy shifters. Asking " What is the difference" one responded "Well it's the difference of owning a Ferrari." Well these guys loved the Mercian frames, all were agreed that they were "quite the stuff". I've lost touch with most of these guys as they moved to other jobs- but happily one still works with me and still has his Mercian.
Mark Cutrufelli
Laurel,MD