I've never taken off the lower, but removing the upper is pretty easy. Took me 2 hours to swap the first time I tried it, now I can get it off and back on in about 60 - 75 minutes.
Just make sure you have a torque wrench that reads in the in-lb range. Don't just convert to ft-lbs and use a big motha. They aren't very accurate low in their measurement range. Also, there is a specific tightening and removal sequence for the bolts. In the FAQ on the main page, there is a how-to on cleaning the intakes which shows the sequence; also found in any repair manual. You should probably replace any gakets just to be on the safe side, but they can be reused. I had my EGR gasket split when removing the EGR valve from the upper.
