Those look more like Tiara cylinders - 550A induction is on the bottom..so it could be a 540cu in motor (stock bores), or over-bored slightly. Those motors are obsolete as far as I know.
I think the Rolls Royce claim is just marketing...
Rolls Royce built some under license. Maybe it was a license built one rather than one built here.
You are right about the induction. It does look more like a 540, and looking at the valve covers, I’m thinking Lycoming.