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.