Without a letter to validate the barrel length it may be difficult to confirm that the barrel is as it shipped from S&W. Some pictures of the barrel crown might help, directly at the muzzle and close up and sharp.

The barrel stamp position, compared to that of one of my 6.5 inch pre-26s, might indicate that the barrel length was shorter. Hope it works out for you, a real oddity if original.

Jeff
SWCA #1457