2 7/8 inch shells are right
They would have 1 3/8 ounce or 1 1/4 ounce of shot.
These were made commercially up through about 1970, as there are quite a few older ten gauges around that only take this cartridge. The last ones I've seen were Remington and roll crimped, with green translucent plastic hulls, they were #5 shot and functioned well in ten gauges that took the longer shells.
The magnum ten gauge is all that is normally available now, and you do not want to try those in your shotgun at all.
If you load for it, the older data for the shorter shells would work, or black powder loads. You would have to trim down the hulls to the proper length, and getting the crimp right might be hard as you would be forcing the sidewalls in for the crimp. I would recommend an over shot wafer or piece of cardboard to keep the shot in. This would not be overly hard to do if you had the original data and used something like Unique or Blue Dot. Hulls for ten gauge are not normally plentiful. Wads are expensive. You would have to cut some wads to make them fit. Wafer wads were what was original, the plastic cups did not exist when the ten gauge was a short 2 7/8 standard.
If you go to all this effort, you can expect to find the old ten to work well. Ten gauges generally pattern very well and the larger payloads hit well too.
