It is hard to tell how wide that slot is just by looking at the picture. So, it is either the bracket for a Twin LNB (110 and 119 only, with no place to put the 129 LNB) or it is the bracket for the newer-style Dish 1000 LNB's that integrate all three satellites.
Ah, you are right. I didn't realize what I was looking at. Given the age, I would guess it was for a twin LNB. So he would only need to get that LNB (and a mast) to get that working for his 322. He has already stated that 129 is more trouble than it's worth (for the limited SD on 129) at present.