I was just looking into this exact topic and Rocky Mountain ATV has a fiche available you can study.
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This is what I see for the R when I look at the steering box and rack part numbers:
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These are the steering box and rack part numbers for the X:
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I must say I'm a bit stumped just based on what I've seen. I also checked the EPS unit part numbers and they match. I was hoping to find a steering stop of some sort on the R, but it doesn't appear to have one.
If someone figures this out I'd love to know what the difference is between the two.