I performed this alignment this weekend. It didn't go as smoothly for me as it should have. The whole concept/procedure here is quite easy but if things aren't moving freely, it can be a real PITA.

1. I think that you can simply loosen the coupler bolts to check for alignment but if you need to adjust (or by more than "just a little"), I would suggest removing them at that point. One problem I had was that by not removing them, the bolts and the "lip" of the flange would interfer with proper measurements/alignment. I chased my tail for a while here.

2. I needed to adjust the "yaw axis" but the engine mounts would not slide freely on the trunnion pins. Age and corrosion were certainly part of the problem here but I suspect that the trunnion pins are somewhat "locked" in a parallel horizontal axis. After a few bashed appendages, I needed to change course. I was also going to need to make a vertical/pitch axis adjustment so I released the locking nuts and made some adjustment there. Then, things finally started coming together and I was able to move things more freely horizontally on the trunnion pins. So my take away here is that you need to release the locking nuts to allow the trunnion pins to turn a little about their "yaw axis".

I hope that from here on out, I'll mostly just need some minor vertical adjustments, in which case this will be a piece of cake!