the other dome was a protective cover that would cover up the servo motor conections, the servo had 3-screws on it where you put the wire in then tighten up the screws, like you do a actuator today.
when I got that feed (this is maney moons ago) that is when I changed from a LNA & down convert to a LNB an if I remember right put a 75 degree on it, was the lowest you could get back then.
also in the little dome will have a antenna that looks like a butterfly that the servo motor turns, now a servo motor of today will NOT fit on that feed, it takes a servo with a square drive sticking out.