The Japanese Autorace frame design is based on 1950s British speedway frames like the Rotrax. If you want you can search for other names as well.
The Japanese government insisted that they raced on tarmac instead of dirt at some point, to reduce race and bet fixing by criminal gangs, and I think they froze frame design at that point. Note the use of an old fashioned knee hook, which had been used by leg trailing riders on the old deep dirt tracks.
A part of a race heritage carry over, I'd think, Ludwig. The gear selector change over from left to right is similar to one of my current design ideas for a foot to hand shift mod for my Harley Peashooter, especially if I opt for a jockey type selector lever on the right side.
I see the speedway heritage in the trainer which of course is a design favorite of mine along with the early flat track and board track styles. Thanks for sharing. Rick C.
I just investigated a bit. Akagi Autorace use small capacity bikes for novice and experienced riders, and people are permitted to enter and try it for themselves, using Akagi's bikes or their own. There are picture and also video galleries.