The Gen Lee Fist
Published in Street Defense -
The Practical Martial Arts Magazine,
Volume 2, Number 3
Manor Books, New York, 1977
Although not Isshinryu, the manner of fist formation is similar.
I wouldn't recommend striking with the thumb knuckle unless
you have trained for it and not much is said about placing the
thumb on top providing bio-mechanical strength in the wrist.
Nice 'stache though.