I've tried to look into this exact topic. from the limited amount of information available on the web I can tell a few differences. the John Deere Quik Trak 600r series is manufactured by Wright. the platform and deck. what John Deere did was take that base and mostly apply John Deere patents to it. some of these include stuff like patented anti scalp wheels on the deck and the quad levers being changed to two more normal ztr style levers. also, the Quik Trak's wiring is done to jd specs. there can probably be easily 100 different changes between those small differences.
but overall, I think someone who has experience with both would be able to tell you more.
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