They made those trailers for many years, starting in the late 1960s, and ending in/around 1980 when IH went out of business. That one looks to be one of the later ones, just because of the large IH decal, that is not the IH with the border and INTERNATIONAL under it like this one:
This would have been on the early models of this trailer, through the mid 1970s.
The tires originally would have been Goodyear or Firestone, smooth rib tires.
I believe only the later trailers had the serial number plate on them, again, probably starting with the *1000/1050 series tractors in 1976, or *82 series Cub Cadet tractors in 1979. I'm guessing, but the '76' at the end of your serial number probably stands for 1976.
That one sure is in good shape. My dad had one just like it, and we used to duct tape the tailgate seams, and fill it with water to water the garden. You'll be amazed what that little trailer will haul!
1951 Farmall Cub, Cub Cadets 102, 104, 1811, 1864, Simplicity Legacy XL 4x4 Diesel with FEL, 60" mower, 50" Tiller