Potential issues:

- Front derailleur: The current MTB FD won't fit the curvature of the road crank (with larger chainrings well). If you put a road FD on, its cable pull ratio won't be compatible with the MTB front shifter. A friction shifter eliminates the second concern.

- Chain line: Standard chainline (measured at middle ring) for road triple is 45mm, whereas for MTB it's 47.5mm (or 50mm for most newer cranks and for frames with oversized tubing). The road crank needs to be spaced out far enough for the chainrings to clear the chainstay. The chainline can be moved out by using a bottom bracket with a longer spindle (though for newer cranks with an integrated spindle, this is impossible).