I remember greasing and threading the bolt in with a battery impact. I put everything on loosely, then worked from the rear, checking as I went. They are stunning if not perfect, I assume they are as good as new Honda but I didn't own any back in the day, my K4 came used with a 4-1 hooker. Out of the three Yamiya sets and one used Honda set I've put on, I have thumped a couple pipes with a rubber mallet through a rolled up towel.
As a racer, I'm used to many aftermarket things not fitting perfectly or an occasional hidden defect appearing later.