It has both a waterhouse slot for internal gel filters as well as a filter thread on the front. The manual shows 86mm, not 90, a real oddball. I recall measuring my own 480 a couple months ago, and realized that an 82mm filter wouldn't work (my biggest size filter set on hand), or really any other standard filter size without a custom-machined step adapter. Of course, there are ways to use large square resin filters; but I don't personally like those. I was simply fooling around, playing with it on my 8X10. For actual field usage, I already have a way more compact and practical in-shutter 450 Fujinon C lens. But Apo Nikkors are stunningly well corrected, so are fun to look through and realize just how much detail there is, given a good loupe.
I acquired a whole set or Apo Nikkors for free from a giant abandoned process camera, during a commercial remodel. I use the 240, 305, and 360 as enlarging lenses.