It used to be the case, but if you look carefully, for lenses from 90mm up, you'll see lots of users putting the lenses on K-1 and other cameras. I'm referring at the "lens reviews" section of the site:
Yes, i've seen it, but I never have seen results that would justify the trouble (& cost) over using regular Pentax lenses. People adapt things like 120/2.0 lenses but it doesn't make too much sense to me, for example 120/2.0 = 60mm = same physical aperture as a 168/2.8 (the 165/2.8 Pentax is far cheaper). Depth of field is already really really narrow with most P6x7 lenses.
My kit was the 45mm, the 55mm, the 105mm, and the 200mm. All were excellent lenses. The 105 came with the body I bought.
My issue was the crop that the penta prism viewfinder gave. I preferred the waist level finder, especially the 45, but vertical shots were impossible. I gave the entire kit to my brother and now use my Cambo 23SF & 'Blads mostly.
Yes, i've seen it, but I never have seen results that would justify the trouble (& cost) over using regular Pentax lenses. People adapt things like 120/2.0 lenses but it doesn't make too much sense to me, for example 120/2.0 = 60mm = same physical aperture as a 168/2.8 (the 165/2.8 Pentax is far cheaper). Depth of field is already really really narrow with most P6x7 lenses.
I think there are two main reasons for adapting other lenses to the Pentax 67. One is for long tele work and the other is for lens character, like bubble bokeh.