Hahahaha, "should I get a letter on it"
Of course you should, this is an extremely rare but "regularly" factory production gun, it's almost the textbook definition of a collectible S&W pistol and the letter will absolutely enhance the package.
Value? Well, I can drop a number but -please- understand and accept the very standard disclaimer before you make use of the number.
$3,575... sold about six weeks ago on Gunbroker. Condition was nearly "as new" and included every original bit, original box and all papers and items. And the biggest part of this disclaimer, it was offered by Woodlawn Boys, a very well known professional collectible gun dealer. Firearms from this seller and sellers of their ilk bring the MAXIMUM possible money in auctions from folks who prefer to spend more because the dealer's reputation is flawless or nearly so.
This price is one single data point, it is not the answer but experience has taught me that this could or perhaps should be considered the highest point on the scale. As such, I would suggest that in a typical market without some odd outside influence... this is a dollar amount that one of us "regular guys" simply could not get in a sale.
PM sent for more info.
You have a rare and historical pistol!