What is the difference between the 821LM and the 821LMB

I’m trying to make an older LiftMaster slide gate motor work with myQ. I know it’s not supported by the newer equipment, but I’ve found a couple of references to a retrofit kit that used to be available. It uses an 821LM (with a modified door sensor to make it work with a magnetic device instead of detecting tilt), paired with a 312HM receiver.
In searching for the right components I found that the 821LM is no longer widely available, but there’s an 821LMB which is actually cheaper… would it work to pair it with the 312HM receiver?
Thanks in advance.

The 821LMB is the same as the Chamberlain MYQ G0301 I believe, they provide the same function as the old 821LM. I am not familiar with the gate motor receiver you mention, but the 821LM, 821LMB, and MYQ G0301 would all be comparable.