New Truck = Bigger Receiver = Unexpected Problem

Update.. After measuring, I need to drop this thing about 1" - I have one more set of holes I can go down, so that should work - but since I've got to take it apart anyway, I'm going to try to find the correct sized shank tomorrow.
Am I afraid of taking it apart? Yes, quite a bit. Are there any gotchas I need to aware of in assembling this hitch? I don't understand the whole idea of angling the ball, etc. I've seen mention of adding washers to adjust the angle, but I see no washers on this thing.