I'm really intrigued by this plane.
The rear handle looks early, and I've never seen another with that sliding dovetail to hold it.
Now you show it next to the Stanley, the bedding angle looks low. That would support the idea of it being designed to work bevel up, so as you say, it would not have needed a cap iron. So I agree - the blade must have been very massive. (I'm assuming that the good fit of the lever cap argues against that belonging to a different plane.) It looks more like a heavy 62-alike.
I'd love to see some documentary evidence of it being offered for sale or patented by someone.