I saw a 5504 years ago and fell in love. It had a dial that was creamy and the dauphine hands and furniture had a slight gold patina. It has been on my grail list since then and I was finally able to pick one up. It wasn’t running and it had a fake crown, but it is serviced and correct now. I am really happy with this one from 1959! it even has the original butterfly rotor on the 1530.
There were also an Everest model (Canada) and an Explorer in the same reference. I think the 5504 was only made 1958-1960, so short run and quite rare. I image that a lot of the Air Kings got aftermarket explorer dials. The blue steel second just pops on this reference.