Welcome aboard.
I hate to break the news to you, but you have a parts gun with a phony letter.

The gun has a long action hammer, but the Mod 1955 was a short action gun.
The barrel rib does not line up properly with the top of the frame because that frame originally had fixed sights.
The mahogany case did not yet exist in 1955, nor during the 5 Screw era.
Those grips are from the late 1960s.
The engraving is not Factory.
The letter is just SO far from being worded properly that I won't even go into it.
Sorry.

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Regards,
Lee Jarrett