Oyeboten:
You appear to have an early S&W .45 Hand Ejector U.S Army -Model 1917 manufactured between September 1917 & April 1918.
The GHS stamp on the left upper rear of the frame is for Major Gilbert H Stewart, the US Army inspector at the time. Later guns had a flaming ordnance bomb mark instead and S1, S2, S3 etc designating the assistant inspector who checked the gun. I assume the plain S was Major Stewart's personal mark.
The serrated hammer is correct for an early production gun.
The chambers were stepped for the .45 Auto Rim, the .45 ACP used the moon clip for headspace.
I'm pretty sure your gun has a replacement barrel:
The original barrel length should have been 5.5 inches.
The barrel would have been marked with the same serial number as the frame. There should also have been a serial number on the yoke, butt, cylinder face and back of the extractor star.
The barrel should be marked 'S&W D.A. 45' on the right side, 'United States Property' on the underside of the barrel, the patent dates on the barrel should include Sep. 14, 1909.
My guess is that your gun was rebarreled with a .455 Mark II Hand Ejector 2nd Model barrel at the factory, originally manufactured for a British or Canadian contract. These had patent dates to 1906 only, came with a 6.5 inch barrel, were manufactured from 1915 to 1917 in a serial range from around 6000 to 74755, the caliber markings were usually Smith & Wesson .455 but may be missing all together.
All of the above fits for the barrel to be available for fitting by S&W in 1917 to a U.S Army contract gun. The fact you have an inspectors mark on the barrel also suggests fitting at the factory. As to why it was passed, I can only speculate. S&W couldn't manufacture enough barrels and were authorised to use up old stock? The original barrel didn't pass inspection and the gun was rebarreled? your guess is as good as mine.
Thanks for posting another interesting piece.