Lars,
This is one beautiful report, thank you!
I never visited that observatory (not sure if it existed in early '90 (when we moved to Australia).
About that 140 mm Newtonian..
I think the mirror kit (primary and small rectangular secondary) was manufactured by "Juraj Vega", optical company from Ljubljana (Slovenia). (BTW, my very first telescope was also "Vega" (refractor ø45 mm, FL 700 mm).. )
This mirror kit was on sale up to mid '70s, and I used it to build my second Newtonian, mounted into a frame built using 20 mm extruded aluminium "L" profile. After the first light, I became aware of the existence of "pinched optics"
(mirror was very thin and had a conical back side..)
Later I gave the primary to a colleague from work (it was not very good, it had strong astigmatism), and I still have and use the secondary in my flip-mirror box.
And about 250mm Newtonian..
In '80-ies, Coulter Optical had 10" mirrors on special (US$105.00). Could they used one of those for second wooden Newt? (nope, now I see on the plate it was home made).
I used one of those for my Dob (now fully motorized)
Anyway.. memories... thank you again.