I a big Standel/ Harptone/ Yamaki fan and currently collecting photos, serial numbers and current condition on existing units. If you have more pics and the serial number off that puppy, please message me.
Harptone made only 300 units across all models for Standel between 1968 and 1969. This includes the 420 s and the 520 s, thinline hollow bodies, the Eagle, the Lark, the 811 Archtop, the B4 acoustic bass, the 1000 S Archtop, and the 400 S electric base. All had 3 levels of finish. Budget had MOP dots on the fingerboard. Mid-level had the dots and binding up the fingerboard and head stock. The pro level added MOP rectangles to the fingerboard. Designed by Sam Koontz, all models including the acoustics had elements of his love for the Archtop Guitar. You don't see many if any acoustics with the curvy back of a Archtop. They were so well designed that Harptone couldn't build a bad one if they tried. nice warm tones throughout the line. even the Dreadnoughts rung jazz riffs like it was born for it. The crown was influenced by the D'angelaco's and was Koontz's calling card. You will find it on the above brands and his own hand made Archtops. He also invented sliding F and sound hole doors to kill feedback on the his Archtops. The first one with this innovation is owned by Jazz legend Pat Martino. That's the short story with some background.
Look at the label. If it says Harptone, your guitar was built in 1968. It took Standel about 8 months to get their own label.