Firstly, here is an interview with Ron by the ASC:
FWIW, IMDB says that Fuji stock was used for season 1, and Kodak stock for season 2. I have to assume that 500T stock was used throughout (that's what I would do!).
I was shooting Fuji at the time. I’ve shot Fuji most of my career.
And what it did basically, with those double 85s in to the negative, it contaminated the black area to a point, but the contrast, that kind of went away, but it was still in the shadows, so people expecting a lot of cool looks in the wintertime, even the overcast… The skin tones stayed, I could control the skin tones, and it just permeated all the greens and browns into this kind of golden feel that we all liked. I think it was that particular time in my career, the Fuji was giving me those kind of colors and Kodak wasn’t for some reason, so it worked out.
And I think one of the other reasons, trying to explain on an audio [interview], what a visual looks like, the way the film was constructed, the way it was designed in colour couplers, if you open up your hands and spread your fingers, and then put your fingers together, and form a little wall, like you’re reading a book, there’s no gaps in between your fingers. That was the way Kodak’s system worked, as far as I was concerned. Fuji, you open up your hands, and you spread your fingers out, and you can see light through your fingers. That’s the way the Fuji worked for me. So there wasn’t a lot of crosstalk with all that light going through all the layers of film - your red, green, your blue, green, reds. And I was able to pull in that yellow and keep that orange, and keep the skin tones, just because of the design of the film which I loved and stuck to most of my career until we went to digital.
This list of Fuji stocks says that the F-Series was not released until 1988. However, the older AX 500T was already available to Ron before Twin Peaks. I'm guessing he shot that, and not the F-500T.