Originally posted by séamuis im sure paul will chime in but the auction says but it also lists spotmatic among the 'compatible' cameras. I doubt it follows pentax sizing but if It fits a K series K mount camera it should fit a spotmatic because im almost certain they have the same viewfinder dimensions. it should be noted however that the dimensions between K and M are only very small differences. and anything compatible with K should work with a spotmatic. A K series is just a spotmatic with a K mount anyway.
Glen:
If it fits a K body it will fit your Spotmatic F. The eyepiece issue is more a problem with the Right-angle finders, since they have a more rigid attachment fitting. You just cannot get the old finders on the M and later eyepieces.
I have purchased from "The Camera Hunter" and was satisfied. I'd bet if they say it will fit a Spot F, it will fit. Maybe the mount is flexible in some way.
As I said, I found one eyecup a couple days ago, but I'm not sure if it is the one I use or a spare. I'll look in my KX bag and in the bits bag after work and PM you.
Paul