That rod came out of a different XR600 zrxer bought with a blown engine. All the information on putting a 650L bottom end in an XL600 is on the first page. I say "bottom end" because the single carb head is not easily used in the dual carb frames due to the centrally located rear shock. Single carb frames have the rear shock offset to one side in order to make rood for the carb and airbox boot. For simplicity, use the XL600 cylinder, head, and cam chain/sprockets with the 650L bottom end and piston.