When looking at this gun, to identify caliber in the absence of other clues, remember the front sight is taller for larger calibers. Notice that the front sight is rather short, but also has a factory profile. This leads me to believe it was a 38/44 HD at the get go. The taller front sight angles the bore axis down, to counteract the rise in trajectory of the larger calibers. Of course, front sights can also be altered, post factory, so always look for that.
This same rule is true on K frame targets, etc. On pre war K frame targets (with the pre war target rear sight, not the micrometer), for example, the shortest front sight will be the K-22 OD, followed by a 32-20 target, followed by the 38 spl M&P target.