You are going to potentially run into a couple problems.
- First, have you made sure the bellows will mount to the K-1? While both obviously use the K-mount, on some digital Pentax cameras the pentaprism housing is too close to the lens mount to allow this bellows unit to attach. I have the bellows, I don't have a K-1.
- Second, although the bellows says Auto Bellows A, you cannot use the 'A' setting on the lens as the contact points are not transmitted back to the camera body. And unless your lens has an aperture ring (don't think it does) you will always be shooting wide-open. Unless the film is exactly flat and parallel to the lens (near impossible), you will likely have soft focus spots. In case you didn't get the manual it says "Note: When you use a Pentax A lens, set the aperture ring at each f-number and do not set it at the "A" (Auto) position.".
- Third, there is no auto focus.
And of course you will either want to use manual flash or green-mode stopdown metering with natural light.
My advice? Get one of the well-recognized K or KA 50mm lens, stop down to f/8 or f/11 and bounce a manual flash off a photographic white card beyond the slide duplicator. While a macro lens might be better, I have had good results with my trusty Pentax KA 50 f/1.8 (stopped down as mentioned, of course).