..as above, it will only go on in one of four positions. And if the steering wheel doesn't point in the right direction remove and re-align the steering wheel, it's a lot easier than re-aligning the drop arm (so long as you've got a steering wheel puller, that is)
Good luck getting the old drop arm off, by the way! If it won't budge smack it on the SIDE with a large lump hammer against a solid surface first.