The plenums come off pretty easy. The intake manifold itself is a little more messy. Be sure to drain some coolant before you take the intake off. It has coolant in it, and it will run into your oil if you dont. Also, your distributor will have to come out. You might wanna check with your local shop to see how much it would cost to have them acid or chemical dipped. Some shop will sandblast thru the ports too. Cant get em any cleaner that that. But, throttle body cleaner & a toothbrush do a fine job too. also, if your have a dremel, gasket matching the ports of the plenums could give ya a little more power too. could sandpaper the runners smooth if you like also, that'll help in keeping them cleaner too.
But, I usually just take off the intake snorkel, start the car, open the throttle ands shoot throttle body cleaner down the intake, while its running, and all the intake snot shoots out the exhaust, and lands in my driveway....
but, I also did take my plenums & hand cleaned, dremeled & sanded 2 years ago. If I was to do it again, I would have them dipped, then dremel/port them, then paint them.