Hey, freezy
I did a search and found out more about your fiberglass dishes versus solid metal onesor metal mesh dishes.
The important factor is how far apart the mesh is. It jogged my memory, as I remember reading several years ago that the mesh has to be closer than a pencil width to get ku. Otherwise, all you have is an old c-band dish.
A possible option is to shine a strong light through the fiberglass to see the mesh underneath. The other option is to strap a combo lnb to the dish and try it on ku.
If it works, you've got a ku compatible fiberglass dish.
I'm using a perfect 10 dish made in 1993. At the time it was installed, it had a combo c/ku band corotor on it so I knew it was ku capable. If you use an early fiberglass dish, you just taking a chance without experimenting first or finding out more from the manufacturer's specs.
I'm presently looking at two early Channel Master dishes. They are the huge earlier models. They may even be larger than 12 feet across. I like them because of the weight and size, but I know it will take a lot of concrete to get them in the ground.