[This is an old 39. Both of the parts I tried were way too small in width to fit the barrel dovetail.]
Mine's not a 39, it's a 39a made in 1951.
IMHO, 1/8" is way too much discrepancy, for allowable "tolerances".
Since there's not a whole lot of pressure on the hanger (unless a clamp-on sling swivel's installed on the mag tube), if I had your situation I would side-shim the dovetail with a very small piece of shim stock & cold blue it to match.