Steve the XL500 79,81 has a steep steering rake 26 deg no need to change it , The XL500 wheel base is 1400mm same as a jawa ,gooden specs
then put some 36mm early XT,TT500 inline forks on it
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and the alloy TT500 model swingarm will work on the frame to, for some weight saving and some shine
Put a XL185 tank on it aswell.
then wack a champion or XR750 seat guard combo on it , they are a cheap dirt tracker plenty of parts out there and cheap as chips, and they seem to honk along aswell .