Interesting find!
- You might be able to find more information on them if you search using MTs8
- They were made by TSKIB SOO, which nowadays is under kbptula.ru
As far as working on them, they are pretty straight forward. Caption Obvious: Make sure you have the correct thin bit screw-driver... it would be a shame to bugger one up.
- They are not that common, than again, I don't think any Mts shotgun is common on this side of the pond.
- The few (2x) I've heard of for sale (in the last 20 years or so) were two barrel set (1x trap and 1x skeet)