I checked back in my FWB info folder and found a post by Joe "Jeweller" Tousignant with an email from Feinwerkbau Westinger & Altenburger GmbH, dated June 2001, saying:
The FEINWERKBAU air-pistols Mod. 65 were produced
from 1965 - 1998, the air-pistols Mod. 80 from
1977 - 1986 and the air-pistols Mod. 90 from 1982
- 1992.
Another FWB email said:
From air-pistol Mod. 65 we produced approx.
145.000 pcs.,
from air-pistol Mod. 80 approx. 48.000 pcs.,
from air-pistol Mod. 90 approx. 20.000 pcs.
I have one of the blocking plates and screw somewhere (not for sale) which I can dig it out if you want pics/dimensions etc?