I just acquired a vintage Gruen Curvex Precision model with a 330 movement. (Turned out to be a 311 movement). The size is an impressive 46mm long (lug to lug) by approx. 20mm wide. The Curvex case is marked 10k gold filled. I remember reading that these old Gruen watches were one of the first in a series of longer models, but when looking closely at the back cover, I noticed what appeared to be a portion of thumb nail tab that might have been removed. I was under the impression that the later models had a tab. Is there any way of telling if the movement might have been switched to a newer case? The overall condition of this watch seems excellent, but the rear case cover made me wonder. The marking on the back cover lip reads Gruen 10k gold filled. I look forward to your responses.