9’3". @ 4 inches thick. A comment in the Clark Catalog was that the 9’3 was the oldest longboard blank in the catalog. The other “Old School” Clark was the 10’3" Phil Edwards @ 4 3/16" and 26 wide. They used to charge you an extra because the rarely kept them in stock.
The adjustable fin makes me think the board dates from 1970 or very early 1971. Most likely the number is 28001, Well after I left Hansen, in 1969. The letter designater A is unknown to me, as to who the shaper might have been.