the buttonhook is a j-rod. it extends from the core of the dish straight out then j's. this one is welded to it's lenghth of 33-5/15, looking diriectly into the center of the dish.
So I would have to set the f/d of 28 of the tube of feed (i think) to be at my f/D.
I think to give it even more support, the brackets could be placed. but this j pipe seems to be a sch 40 or 80 pipe used.
I will take a picture of it tommorrow to show you what it is. Plus it canrotate for a degree setting needed,,, I do not know but if I use a 20 degree lnb I would have to turn this pipe to have the degree needed.
Edit:
I do not have it up yet. I was concerned about this lnb,,,, or as you said "LNA". That is one reason why I did not get it all hooked up.
once get this cleared,,,, I just need to buy the LNB, and the wire, Then get my ground work going.