Shirahone Onsen from Matsumoto (summer)

I'm trying to find information on how to reach Shirahone from Matsumoto effectively.

So far I figured out that there is a bus from Shin-shimashima Station via a Transfer in Sawando.
I don't know if this schedule is valid but it says one of the buses requires a reservation.
However the link to the reservation is dead.
https://visit-nagano.alpico.co.jp/timetable/matsumoto-shirahone-onsen-...

The japanese website currently doesn't list any schedule for summer:
https://www.alpico.co.jp/traffic/local/kamikochi/shirahone/

My question is also if I can take my fairly large (70x50x30 cm) suitcase on the bus. There is no information about that.. (the FAQ says it should be listed at each schedule what the luggage rules are but there is none).

Has anyone traveled this route (on the summer schedule) and can share their wisdom?

The details for 2026 summer have not been published. I would assume that it is the same or similar to last year, when you had to transfer twice, and there are only about four good connections per day.

Many buses in the area have a luggage room for larger luggage under the passenger room, but I am not sure whether such a bus will be used on the Shirahone route. Inside the passenger room of the bus you should avoid anything bigger than carry-on-sized luggage. Specifically:
- not heavier than 10kg
- not more volume than a 30x30x30 cm
- no dimension longer than 1 meter