Thanks, guys. In answer to DanOnRoute66, yes it does have a selenium meter, so it looks like it might be a 3A. Plus it has a 5cm Jupiter-8 lens, the serial number of which also starts 56. I'm not sure if that's significant.
I'll check out those sites konicaman, and I understand already the attraction of FSU cameras. I've had my Kiev for years but have only just got round to playing with it - or should I say, making sense of it. Great fun though, especially without instructions! It makes my Mamiya RB67 seem like an early learning camera.