Electrically, that is probably the part. There are two kinds: Linear taper and audio taper - we want linear taper. If it's an audio taper, the entire fan speed range will be in between two fan switch positions instead of five. Usually, a linear taper is assumed unless specified otherwise, hence I think it's the right part. Piher's product pages describe many such pots with a "PT1Nxx" series part number, all of them are described as "linear taper" - so I think it's the right part.

Physically, it may not quite fit, but I suspect you could spread/contract it's solder-legs and make it fit, provided the shaft from the control fits the hole in the center, and if not, a simply modification with a file may do the job. There are a handful of "PC mount pot" sizes but they don't vary by much.