That sure sounds like a different adapter plate. My adapter plate doesn't have any pins. And it didn't come with a locking washer as you described. In fact it didn't come with any washers, just the o-ring seal.
I received an email from Lawrie Alexander of Moss that seems to have clarified the cause of my problem. When I removed the old canister filter and inspected the face of the oil pump, I couldn't see a groove that the seal ring (o-ring) should slip into. When the canister came off, there was also an o-ring that came with it. According to Lawrie, there is a grove but apparently an old o-ring has completely filled it and due to the difficult viewing of the seat, I was unable to detect it's presence. So now I need to pull it all apart again and use a dental pick to extract the old o-ring. At least it supposed to be cooler this weekend.
I'll post again after I've confirmed this and made it right.
Dave.