I'll go out one day this week, get pictures and try to figure out how to post them. It does have a Purdey-style button fore-end. I'm not sure what you mean by "fences around the strikers", so I'll have to say I don't know. I've handled and looked it over and it most certainly does not weigh 8 lb - it's a lot closer to 5 than 8. The barrels are 28 and a fraction inches, so they could be either 71 or 72.5 cm.
I did write down the marks on the flats. Serial number, if you'e interested, is 506XX-1. The "-1" is on the barrel flat. The same serial number 506XX appears on the inside of the forend, but with a "-6" suffix.
The model number (taken from the flat of the left barrel) appears to be MB-20. Below the model number, it appears to show a 70mm chamber - the inscription says P (Russian "pi") 70. Choke in the left barrel ("YOK") shows 15,6 over a line over 15,0, which I take to be a light full. Choke in the right barrel appears to be cylinder, as there is no "YOK" marking but it does show 15,6.
There are more marks but they're all in Russian script.
