Mystery Carb - Anyone??

I got this carburetor as part of a CB500 true basket case but have NO idea what year or bike it belongs to. They're 29mm Mikunis, but beyond that, I have no idea, I cannot find a model number inscribed anywhere on these carbs, although there is also a "140" inscribed on the butterflies. Honda uses Keihins. I have NO idea what these carbs are - can anybody enlighten me??
 

Not sure from the pics you posted. Will say they appear to be CV type of carb and not vm type. The info/number on the buttgerflies is an ID for them  You say they are Mikunis 29s but that there is no markings on them? What makes you think so? Can not tell from the pics if they have an accel pump or not. but they do have 2 jets and not 3.
Post some more pics if you can

I've been doing a LOT of research and believe I have found them - they appear to be Mikuni BS28-5K5-00...these carbs can be found on 1980-1983 Yamaha XJ550's, Maxims and Seca models, and possibly others. They are in really good shape, as old as they are...