I would ask if you have seen digiscoped results before? Just something to look at before you spend a lot of money. A few years ago while visiting Magee Marsh during the warbler migration I had the opportunity to connect my camera to a Swarovski scope and take a couple of images of a nest the Swarovski reps had sighted. They were not keepers, but of course I'm sure you could do somewhat better with some practice. Here's also a
comparison article. That article is a little dated, and maybe some advancements have been made.
I'm sure you know about the Pentax PF-CA35 K mount adapter, but you already have an eyepiece that you would like to adapt. You might need to get somebody to make an adapter to go from the 43mm to an M42, which is adaptable to many camera mounts.
Good luck, hopefully somebody here may have some experience.