I just recieved my K-var order, including one of the ten round Bulgarians. The floor plate and follower appear to be identical to those from a 30 round waffle mag that I ordered from Magua industries many moons ago. As expected, the spring is only half as long.
While examination and comparison of the two sets of parts is almost certainly legal, going much further probably isn't. We may not agree with the law but we are still bound to observe it, so I think I'll wrap everything back up and save any further experimentation for after the ban.