Ottis, I'm probably the only member of this forum that has actually been to the XB3 factory in Kharkov. We bought a few for our Ukraine Bicycle Project. Very few ever make it over here to the US. When I 1st went there in 2000, they had a sign outside commemorating their 75th year of operation. So that would make the start of their factory in 1925 or earlier since the sign was probably a bit older than new in 2000. Those lugs on your frame look similar but not the same as the lugs on XB3 frames I'm familiar with. However my point of how old the factory is can mean that they might have used a different style of lug in earlier days. I'm not where I can look at my pictures of their museum where they displayed bicycles from their past. It might be awhile before I can get to them. This factory was beyond huge and 4 long buildings took up an entire city block. They told me at one time they had a production rate of over 1 million a year. It was down to a few hundred in 2000.

Frames can last a lot longer than parts and I wouldn't be surprised that an immigrant out of the former Soviet areas put some new parts on an old frame. I understood that all the parts except tires were made in their plant and those parts were not that well made. I also wonder about other bicycle factories in the former USSR. I've heard they existed but don't know brands or where any were located. And I wouldn't rule out old Scandinavian bicycle factories either.