In reply to I'm surprised to see no by mybulova_admin
I agree, the case was probably made by a contractor, or is such limited quantity that Bulova never stamped it. I sent Geoff a picture of the case between the lug and it is stamped 278 and the stamping looks non-uniform like it was hand stamped. I'm sure he will upload the pic for you.
I also discovered that the watch originally came with a screw down crown, and the stem, crown and that little tapered tube is not original. The tapered tube under the crown is a sleeve from a small pocket watch just used for a spacer. I'm sure that finding the original screw down crown will be harder to find then the watch itself.
In the pics I sent Geoff shows the threaded tube inside the case, The tension ring being cast into the case and the serial number for you to see.