Here’s the datasheet and wiring diagram for the M-69. Received this straight from Gamewell-FCI earlier this afternoon. This document confirms a lot of the speculation people had about it being a part of the Century Series and so forth. It also lists all of the design variations and options.
Massive kudos to the Gamewell-FCI tech team. Fantastic people, very friendly and helpful. From looking at the long email trail they had to do a lot of digging to find this!
If you want to view the full sized document I put a copy here: http://kcin556alarmwebsite.weebly.com/gamewell-m69-datasheet.html