Montefioralle in july without a/c

Montefioralle is just above Greve.
It's a about 400 meters above sea level (1200 ft) not 400 ft.
In any case in July it will be hot as hell even at 400m a.s.l.
Whether you'll be fine without AC will depend on your tolerance level for heat. Italians' tolerance is very high.
When Italians say it's not hot, it's because they consider it hot only when it's above 80 degrees F inside the house (27 Celsius), and a lot of Italians set their AC thermostat at that value (or even higher). But most Americans would consider 80F too hot.

I don't think there is a considerable difference between Greve's temperatures and Montefioralle, at most a degree or two during the night. Greve is at about 250 m above sea level (750ft)

Italy in July=hot

As Roberto said, it is all about tolerance. A pool is nice, but unless you are sleeping in the pool, a shower works the same. Keep searching for AC, you'll be glad you did. I am assuming you will have a car, so broaden your search.

Thanks! We are three families meeting in that area so my search can’t be too wide… I’m looking at the stone walls of the farmhouse and trying to convince myself it will be cool with the fans 😂

It is said that you can do a lot to keep those thick-walled houses comfortable by keeping windows and shutters tightly closed in the daytime. I have no experience in such accommodations, so I can't vouch for that. I'm very much a budget traveler. I'll happily take a closet-sized room with a single bed and a view of an airshaft, but I insist on air conditioning just about everywhere in summer. For one night, if I absolutely had to, I might compromise, but I can't imagine the misery of six nights in a non-air-conditioned room if I couldn't somehow, magically, keep it from heating up in the daytime.

I have plenty of experience with ancient homes with thick walls.

They get hot on the top floor (next to the roof) and on the southern side

They might be a bit less hot on the bottom floors but they aren't cool.

At night you need to keep the windows wide open, and maybe you will be able to sleep, between midnight and 8am, when it's cooled off. A lot will depend on what kind of breeze they get in Montefioralle, in that specific house, and whether it's shaded somehow or right in the sun.

We were in Florence last June and had air con. I would not go back without it.
To decide for yourself, go to a weather website like weather underground and search for the historic weather temps in the area, during the time period for your stay.