I do enjoy projects like this, and look forward to watching it come together. I also am new to sidecar things, but have a bit of knowledge about Harleys.
This shows how your sidecar was originally mounted to a big twin rigid frame, there was no swingarm. The lower SC mounting points are part of the bikes frame, two loops on the front down tubes, and two bosses on the axle plate. Rigid frames from 1936-1957, although there were many changes through the years, are the same basic platform.
With the first big twin swingarm frame in 1958, the lower rear SC mounting point moved to the swingarm pivot area of the bikes frame, and has been there since. Sidecar chassis from then on no longer had the large rear mount or mechanical brake linkage tube. This is the part of the LE chassis that will need the most mods to fit a swingarm bike
Neat project, and good planning already!
