Thanks Spec. I have some of those documents and would not be able to setup the alarm system without them. Several I have not seen and are a good reference. I will make sure I keep an electronic copy of all of them. Unfortunately none of them talk about how the panel and keypads talk to each other and I understand why they might keep that information to themselves. Most people shouldn't need to mess with what they have and it is probably more sensible to upgrade to a newer panel to get wifi or mobile support.
I gave back the oscilloscope, but was lucky enough to find something when I posed a question about controlling these signals in a raspberry pi forum. Piscope. Looks I can use a raspberry pi with software created by someone smart to create a oscilloscope capable enough to do what I need to do. There are also libraries there I can use to manipulate that data signal.
My next steps are to get the pigpio libraries and piscope software on my raspberry pi, build the simple level converter and see if I can duplicate what I saw on the scope. From there I can use the libraries and capture what the panel is saying and eventually talk back by modifying the data signal. More shortly. Thanks!