Surface  Suggested by jerseygirl 

Old T-26 release which came in 2 variants, Rough and Smooth. Hard to be
sure from your sample, but I'd guess this is Smooth.

Can't find any useful links, sorry.

Don't worry, jerseygirl.
Any help from you is always appreciated. Thanks to your info I will look it up on the net and see if I have any luck.
Thank you so much, as always, for your selfless help to the community!