Correct crown for this Bubbleback

[jlmnjem]

I took this watch to a local dealer this morning and he believes it to be an authentic Bubbleback, but the crown is incorrect (no markings visible). I've looked on eBay and there are several different crowns for Bubblebacks with different markings. What would be the correct markings for the crown for this watch?

Also, would anyone have a guess regarding the model number? Could the model number be determined by removing the back. The dealer plans to do that but it will be later this week before he can get to it.

Rolex face.jpg