Ku - the reflecting layer in the dish doesn't have any very big holes...if any at all.
C - the reflecting layer may be a grid, a mesh, or have holes too big for efficiently reflecting Ku signals.
Tx - it is very accurate, and won't send signals to the adjacent satellites in orbit. (and certified as such! )
Rx - it's a dish. May have more run-out or surface inaccuracy (just guessing. I suspect they come from the same mold)
These are all offset 6' dishes, made for reception or two-way communication on Ku band.
That big finned canister looking like a paint can, houses the transmitter and receiver front end.
So, if your dish has the paint can, your dish is certified for transmitting.
Yes, you can -
use- a 6' to receive C-band. It is about the smallest size I'd recommend.
I've seen pictures of that dish equipped with two or three different LNB mounts.
One like Linuxman's pictures, is a big steel assembly, with no side support arms.
The other, is a smaller lower rod, with two side support arms.
Since both have been shown with the paint-can transmitter, I'll suspect they represent different years of production.
See also this
thread by Pendragon, where he put his on an H-H mount, and matched a late-model Ku LNB to the original horn, for some serious Ku signal suckin'!
Here's another thread, where Linuxman put
several Ku and C-band LNBFs on his fixed dish.
Lots of ways to skin a horse. What did you have in mind?