RadLocs were introduced on the 2003 models if I remember correctly. The rail for the RadLoc is a single aluminum bar and the clamp encircles the frame.
I don't know if a RadLoc could be retrofitted but I know at the least that the old rail would have to be removed and the new rail attached. A quick call to Hayes, KS should answer the question.
BTW, 2003 V-Rex' were pearl white.
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Keep the chain tight!