I am not sure about Bulgarian assembly; not impossible, but not very likely (Romania - yes, by ARO). At least, all the lettering I could make out in the photos are in Russian (which is different from Bulgarian). Bulgarian title is okay - many of those were sold in former Warsaw pact countries by Soviet military. I almost bought one from Poland.
The manufacturing was moved to what was to be UAZ in 1955 or 57 - but I've never heard of one called UAZ-69 or seen it titled as an UAZ-69.
Very cool in any case. I want one.