Hey Doug-welcome! These are unique and delightful airplanes and there is a wealth of knowledge on this site from folks who have a lot more left seat time than I.
You might try Essco and see what they have in AFM’s (if you can call them that). As you might imagine, the info is pretty sparse and before the FAA mandated more in depth AFM’s.
Finding a D (or even more rare a C) with a 550 will be a challenge, but I am sure that if you are patient you can find one. An alternative is to find a C or D with a 520 that is at TBO and send it out to a custom shop and have one built up for you. LyCon in CA has an excellent reputation for building a blueprint engine.
I highly suggest you speak with Dean Siracusa as he is the ‘go-to’ and knows who has planes for sale off market as well as on market.
Happy to help so please reach out.
Best-
Ed