Unfortunately the manual is in black and white, but the model number is 139.54920 (according to the manual - http://i.sears.com/s/d/pdf/mp-tc/10022781/prod_2188472512), and model number 54920 (according to the website - http://www.sears.com/craftsman-1-2-hp-belt-drive-garage-door-opener/p-00954920000P?sellerId=SEARS&prdNo=1&blockNo=1&blockType=G1).
I’m at work so I can’t physically go look at the opener at this time. The opener did come with a Craftsman Gateway which is what I’ve tried to pair to Alarm.com to begin with. Given all the gateways are made by Chamberlain I assumed they were universal.
My research says this unit will work: 828LM (https://www.liftmaster.com/for-homes/accessories/myq-accessories/model-828lm)