Unless the vertical elements are perfectly plumb,
aiming directly south, and of the right diameter, it will probably be better to fabricate some kind of standoff mount anyway. You need to mount on a pole that will allow you to turn the whole assembly on the pole, and this pole should be plumb, or else it will make it difficult to align.
Something like this might be appropriate, but you'd probably want to figure out a way of making sure it's plumb:
