The problem with mixing the two is that a mtb frame uses a 73mm hanger tube and a road frame uses a 68mm tube. As I recall, some Shimano cranksets include a spacer and can be fit to either, but the R600 doesn't. I wouldn't try to use the two together. 5mm is a significant fraction of the retaining bolt threads.
You could try 'facing' the tube down 5mm, but if you're already hitting a stay that would just make it worse.
What chainline are you targeting? 42mm?
Are you changing from a triple or a double?
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