I do the Colt SAA thing. If the serial number matches both, the letter and the gun, it is very common to have a SAA that doesn't match its letter. The SAA is considered a "modular" design and as long as the frame is not out of spec, it is completely rebuildable into any configuration. Even custom ones. It was also very common for dealers to have new guns nickled for customers. And, for owners to refinish them to their tastes.
If the number on the letter does match, the gun has been modified and refinished.
Unfortunately, unless the customization was done by a very few experts (with documentation), or owned by someone famous (also with documentation), the value is completely ruined.
Even in original condition, 1901 is after all of the highly collectable SAA types (black powder frame, "pinch" frame and US Army marked) and 45 is the most common cartridge. In perfect original condition with completely matching letter it could be worth around $10,000 (perhaps more).
Unfortunately, no matter how good it looks, it is a non factory re-finished gun and not even in the original cartridge. Unless it has some kind of special history, It has no collector value at all.
Value wise, between $1,700 and about $2,500, perhaps add a grand for engraved. The old guy may have had it appraised and was told "seventeen hundred" but accidentally heard it as "seventeen thousand".
MLG