After looking at the pictures of the stock more closely I would use at least two street 90* elbows and a 45* elbow. You might need a male to female extender, but I am not sure since I don't have the parts in front of me. The easiest thing to do would be to drill a hole on the bottom and on the right side of the stock for the fittings. Then have the air line run down the side of the marker to the valve.
Another option would be to route the line through the shell and then have it come out above the where the it would go into the valve. Heck if there is enough material on the shroud I would mill out a slot for some macro line to run down the inside of it to the valve. If there is only enough room to do half the diameter of the line there should be enough metal on the 98 to mill out for the other half of the line.