Second picture, all the way to the right. That's the
121/119 assembly.
The horn and LNB on the right in that picture, is DBS (circular).
The right lnb needs to be changed out for FSS (linear).
Don't have that assembly to measure the spacing between them, or we could calculate if they'd be proper for your location and choice of birds.
The specs of the dish have a bearing on LNB spacing, too!
So, focal length is necessary to do any math.
But at least there's a picture of the hardware in question.