Late to the game on the long 16-gauge shells subject, but while the "standard" 16-gauge shell was 2 9/16-inch, they were offered in 2 3/4, 2 7/8 and 3-inch. Back in the day there was a series of articles by Gaucho of his trip through the south hunting with a 2 7/8-inch 16-gauge, but I have yet to see a box of 2 7/8-inch 16-gauge shells. This 1927 Peters catalog lists the availability of their High Velocity in 2 7/8-inch lengths --
HIGH VELOCITY loads 1927.jpg
Here are various boxes of 3-inch 16-gauge shells --
HIGH VELOCITY 16-gauge, 3-inch, #7, Blue Wing Teal.jpg
IDEAL 16-gauge, 3-inch, #7Ch, DuPont Smokeless.jpg
PREMIER 16-gauge, 3-inch, #8Ch, Hercules Infallible Smokeless.jpg
ARROW 16-gauge 3-inch 02.jpg