Re: Old russian nspu
I think per the nomenclature you are talking about a 1pn34 which sometimes went by the name nspu (the 1pn58 went by nspum). If you do have a 1pn34 unit its a cascade style gen1 unit, comperable to a US pvs-2.
If you can post pics here or email them to me, since I don't check this site too much I may be able to help further.