A bone stock bike is worth way more than one that has been customized in most cases. 71 is first year for OIF making it somewhat less desirable but still very collectable. The 70 on back bikes are more popular but not making the 71 and up worthless. Best way to turn an OIF bike into a bobber is to buy a custome frame and swap out the engine or get a 63 to 70 frame and start with that. Maybe a bolt on hardtail to go with it.I have seen frame and frame sections on Ebay fairly cheap. If you want a hardtail you may pick up a 63 to 70 front section fairly cheap. A word of advise on the hardtail, weld it on.

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