Neither o nor 0 is crossed in the architectural lettering - that's the letter Ø. There's a few other non-modern-English letters in that initial alphabet line as well.

https://en.wikipedia.org/wiki/%C3%98

That's pretty close to what we were taught in my high school mechanical drafting class back in the late 80's. I remember being told that it was designed (e.g. big openings on the A) to survive being reduced to microfilm and back.

Chancery cursive was used for English government records. It's a speed form, not a decorative one. There are computer fonts for it, but they seldom capture the original look.

Isn't that the diameter symbol, and not o, O, or 0?

http://www.fileformat.info/info/unicode/char/2300/index.htm

From its position among the regional accented letters, I'd assume it's the Danish/Norwegian Ø

http://www.fileformat.info/info/unicode/char/00d8/index.htm

Yes, it turns out it isn't #\O. I missed the real #\O at the beginning of the same line.

the crossed O there is a distinct letter.

neither lettering formats take distinction of O and 0 into account.