Nutone LB55 & Ring Pro Installation

Hello! I recently purchased the Ring Pro and am just a bit confused on the installation. I believe, based on the list of compatible doorbells, that it should be ok. My Nutone is listed as “Nutone Scoville”, but with a bit of internet searching, it appears that it is the LB55. I don’t see anywhere where it isn’t compatible, the one listed as Non-Compatible is the LBC55, which is the model with a clock in it. Thoughts? What isn’t straight forward to me is where the transformer screw is to attach. I also believe I have a separate power source installed in the basement. Any help / advice very appreciated! Cheers.