I also believe it is the variety WB-1 Large "S" from Bill Bugert's "Liberty Seated half dollars
Vol. 1 San Francisco" book. I've quoted a few passages from his book below. You can get free PDF copies of all of Bill's excellent references at The Newman Numismatic Portal.
The last time that Hub 1 was used on SF half dollars.
1864-S is a scarce date. With four distinct mintmark sizes and styles and two very scarce die marriages,
this date is very interesting and challenging to collect. The obverse dies have date position variations or
readily recognizable die diagnostics that permit quick identification.
Some high grade 1864-S half dollars were contained in the Guatemala hoard and can be identified by their harsh baking soda-like cleaned surfaces. Five die marriages are known. This one being the most common.
It does have that old baking soda cleaned appearance as well.
Guatemala Hoard Coins:
In his Complete Encyclopedia of US and Colonial Coins, Walter Breen discusses a large cache of Liberty Seated half dollars
, known as the Guatemala Hoard (for the location of the find), and it is worth repeating here: ".about 1956 unidentified individuals discovered an immense hoard in Guatemala, reflecting mass wartime (i.e. Civil War) shipments of coins as bullion. The Guatemala Hoard coins are readily recognizable: They are dated between 1859 and 1865 Philadelphia, and between 1860 and 1865 S, most often between 1861-1862 from either mint, ranging in grade from VF to nearly mint state, all cleaned with baking soda or some abrasive. There were many hundreds of each date, possibly a couple thousand 1861-1862. As there were not later date coins in the part of the hoard I saw (at New Netherlands Coin Co., 1956), most likely the hoard was buried about 1865 or early 1866. Either there were no 1866 S No Motto coins, or they were fished out beforehand; but I have seen none matching the hoard coins."
Don Taxay, in his Comprehensive Catalogue and Encyclopedia of U.S. Coins, also mentions the Guatemala Hoard with minor differences in the included coinage dates: "Note: "P" mint half dollars ca. 1859-1865 and "S" mint half dollars ca. 1861-1865 are now relatively common in scrubbed unc. due to a large Guatemala find."
Another source indicates 8-9 thousand XF to AU half dollars were found in 1948 in jars. Dates were mostly 1853-O and 1861-1863-S.
Whatever the exact dates and mints of the coinage, high circulated and mint state grade cleaned S-Mint half dollars of the early to mid-1860's can be found today.