An adjustable stem may work, its a bit heavy and will not be as stiff.
You can get quill stems down to a couple of cm in length. Is it for a 1" or 1 1/8" steerer?
To replace, you usually have to take all the fittings off the bars and slide them through the clamp, then refit everything. Front-loading clamps make life much eaier.
One of the better touring-style bike shops may help with a short quill.
Try Harris, Rivendell etc.
When comparing your MTB position to your tourer, make sure that all the points of contact match up. Check the crank length, the pedal-saddle relation, then the saddle-bar relation.