Once the side arms were bolted in place it was easy to get the correct length of the cross brace. I cut a piece of 1 inch square steel tubing to the correct length, leveled it so it would be flat (horizontal to the road) while the bike was moving, and welded it in place. Voice of eperience here...after about 2 years (2,500 miles) I noticed the square tubing around the Heim end was bending under the stress. I welded extra plate to both the front and back of the tubing to reinforce it. In the 2 subsequent years no problems have been observed. Do yourself a favor...either use very heavy tubing, or add reinforcements.
Once I had the hitch in place I decided to add a 2nd cross-brace that would utilize the Vetter baggage cross brace. One problem I found when using flat stock for the side arms...the hitch flexed side-to-side more than I expected. I bent a piece of 3/16 by 3/4 flat stock into a long, wide "U" so that I could weld it between the side arms and clamp it to the Vetter brace. This worked very well, eliminating virtually all of the flex.
I drilled 2 more holes in the cross brace and added cast eye hooks for safety chain attachment points. The tubing around these eye bolts was reinforced with small pieces of 1/4 inch plate welded to the squre tubing.
Finally I drilled 2 small holes used to attach the trailer wiring connector. I used cable ties to run the wiring up the right-hand side arm up to the point wher the wiring disappears under the seat, there to plug into the bike's wiring harness via home-built bullet-style "Y" connectors.
Thats it. I painter the hitch a nice flat black, bolted it in place, and have been pulling my trailer with it since the spring of 2000.
Artist Rendition of Side and Drop Arm Assembly