Hi,
I came across your post with some interest as I actually owned a Sprite Sachs back in 1973 when I was 15. I think it was a 'J' reg. When I bought it it was already a bit tired so I stripped it down only to find the headstock twisted. I managed to straighten it between two trees with a length of pipe. My feeling was that the frame looked strong but wasn't. I re-painted the frame and put her back together. I think mine had an orange fibreglass tank. I remember the REH forks and hubs, big but not much good. The forks were very odd in that the seals sat in a groove that meant you had to distort the seal to get it in. The only way I got the forks to work was to put gaiters on them and let them run oily otherwise they suffered chronic stiction. I ran some junior trials on it. I remember the Sachs engine as its strong point, strong, reliable and easy to start, she flew when you gave her some revs. I have a photo of me on her somewhere. Good luck with your project!
Cheers,
Rob