Put it all together today. Temps in the garage were just barely 50F but I put on an extra sweatshirt and went to work. I torqued the bolts on the receiver to a tight 3 finger mechanics tightness... actually 4 fingers tight with my hand close to the ratchet head. Then I installed the square tubes on each side. There was a bit more adjusting to do with the flat bar on the ends of the square tubes to be tight and flush with the spacers AND the bike frame. The bolts to the bike frame were also torqued same as the receiver bolts. Since these nuts and bolts are a metric 10.9 grade hardness I could tighten them even just a little more without worry of them being over torqued.
Then came time to mount the end plate on the ends of the square tubes. The holes at the ends of the tubes were not perfectly aligned so I inserted my round file in my drill and filed them a bit to enable the bolts to be pushed in without too much pulling in on the tubing ends. There is still barely a little stress on the tubing ends pulling them inward just slightly. Since the end angles of the tubing was about 1 to 1.5 deg off I added a washer to the bottom bolts between the end plate and the square tube ends. When all the bolts were tightened I put a vertical level on the end plate and found it was less than 1 deg forward at the top. This is where I wanted it to be since that will level out with a little extra sag on the rear of the bike when loaded in the storage box and in the trailer. I will leave the extra length of the bolts alone for now since the long receiver bolts are behind the mud flap. The end plate bolts are well outside the rear tire so no worries there.
In the picture where the trailer is hitched to the bike I put a board under the rear wheel same as is under the front wheel of the bike to level it. That shows close to how the trailer will sit behind the bike. I'm sure a little more sag in the rear suspension will have the front of the trailer down just a little but it looks like I might not have to adjust the trailer tongue down any. I have the receiver 2 inches lower than the original owner had it. Will see when I have a test load in it. Also in that picture the single safety chain (all that is needed for this type of trailer) is just hanging. I am waiting for a special threaded quick link that will be used to hook the safety chain to the receiver. While the trailer was hooked up and the electrical harness plugged in I tested all the lights and everything works as expected.
With all the bolts tight I grabbed the end plate of the hitch and wiggled it up and down, left and right, forward and back as hard as I dared. This hitch as it is so far, without the hanger bar, is the strongest stiffest sturdiest hitch I've had on any bike... maybe my old Gold Wing hitch was about the same but that one was bolted directly to the frame under the saddle bags. Other hitches, like on the ST1100, had more wiggle than the hitch I just installed on the AK. I could wiggle the entire bike but the hitch itself did not wiggle at all separately from the entire bike. The bike and hitch frames are one unit. I really don't think any way of adding a hanger bar will make any difference in the sturdiness of this hitch.
The next thing I plan to do is to put some load in the trailer and in the storage box on the bike and go for a few test rides so check how it tracks behind the bike. Once that is done, if all goes well, I will be removing the hitch parts again and cover all the parts with a rubberized coating. Then I'll install the hitch frame permanently.