Your Sanger Plane was helped by the Japanese for the exchange of the GO-229 technology with one airplane delivered and one in parts seen in a photo. All the Japanese had to do was build this large rail to launch this machine, but it was also documented as the MOST difficult man power operation of its time do to its specific design and labor intensive build.
I find your assertion hard to believe. The Sanger never progressed past the design stage so why would Germany want Japan to build a launch rail? The Japanese had no greater skills at fabricating steel structures than the Germans.