* Sounds like a "w" block 1937 transitional 2nd Variation. The script "w" actually looks like a "nv" sharing a common leg on first glance.
* Pictures of the frame's S/N would confirm this suspicion.
* I show a 51xx "nv"(aka "w") recorded as a 1937 chamber date bearing dE/63(2) acceptance stamps with a Test Proof Eagle (style 2), all blue, wood grips, & humped frame. If this mirrors your pistol, I'd be appreciative if you reported the numeral or numerals stamped on the inside of the removable side plate and the mag's S/N including acceptance stamp.