Any special issues with putting a wider internal gear hub in a narrower alu frame?
Do not use a mis-matched internal geared hub for your frame.

You risk damage to your gear hub, your frame, or both. Aluminum frames are much stiffer than steel frames, which is good for good for riding, but it is also prone to cracking due to this stiffness (when compared to steel's malleability). Even if you do fit the part, it will be a weak point in the frame.