Will this work on ISD990?
No, it will not. The down limit switch for the ISD990 would be 33950S.S.
Will this work on model 2020L
Yes, it will.
Will this limit switch work with an Aladdin 1020 chain driven opener? It looks exactly the same, but I don’t see this model listed.
Yes, this will work for the Aladdin 1020 model.