2. I first came to Kyoto on a school excursion in 1946.
means "I" came to Kyoto for the first time in 1946.
No - it's ambiguous in written form and suggests that you have been on several school excursions to Kyoto, and that the first of these was in 1946. It is possible you had been to Kyoto before that, but this was the first time as part of a school excursion. Spoken, with the proper emphasis on certain words; and 'on a school excursion' with a break after 'Kyoto', and before 'in 1946' , and the meaning you wanted to convey might come across. It would come across then more as: "I first came to Kyoto - (on a school excursion) - in 1946.
compare:
I first came to Kyoto in 1946, on a school excursion.
This sentence means, your first visit to Kyoto was in 1946, when you visited the city with other students as part of a school excursion.
I came to Kyoto first on school excursion in 1946.
I think (this) Sentence means "my" first visit was Kyoto on the excursion in 1946,
The meaning of this sentence is not clear.
compare:
Kyoto was the first city I came to on a school excursion in 1946.
Now it is clear that you visited several cities, and that the first place you visited was Kyoto.
Other posters may be able to suggest even better wording of this sentence than I have come up with! (lol)



