Likewise! Yeah, there aren't a lot of folks working in this space π
Cool project! Sounds doable - I haven't worked with a Sceptre terminal specifically but other terminals I've used just did standard RS232 serial. By "call in" do you mean via a modem?
For any unfortunate folks without access to NAPLPS hardware I've found Microstar's PP3 client works pretty well.
https://dspace.library.uvic.ca/items/1cf4340d-88b9-4dd8-a99b-871634dd8294