I consider heavy trimming as anything that requires you to actually cut something off. This means taking a good chunk of the front bumper. I've included some links on the bottom that Timber725 generously provided. Not sure how much you really need to cut as it all depends on what kind of tread pattern you get. The 285/75/16 MTR's really took a bite out of my front bumper (when stock) that everytime I turned into a driveway I heard the rub (sounds like baseball card in the wheel of a bike - chatter but loud). Trimming that entire chunk will kill this sound.
The UCA's will help with a few things:
* Avoid hitting the coils (stock or aftermarket, both with 3" lift) on the uca. Not sure if this will happen if you drive w/ your swaybar on though as I took mine off right after so that could be a significant factor since I have more droop w/o the swaybar attached.
* Should give better clearance on your tires but I'm not sure exactly how much. I never had a chance to do any comparison since I pretty much got the arms around the sametime the tires were added. Go figure.
Some other things to note:
When I went to Pismo last year I did encounter this that nobody else has at the moment. My setup at the time was the 3" lift, UCA, 285/75/16. Apparently during one of the runs under heavy compression, I sliced my driverside rear tire (enough to take a significant portion of the treads off). It's hard to explain but based on the rub marks it completely hit the rear door (the cladding - since mine is the unpainted version) look like it just decided to cut the tire up like butter. Needless to say, that tire got retired rather quickly and now sits as a spare for the trail only.
285's can be done and I recommend it to anyone that wants to as getting 265/75 just doesn't compare in terms of footprint when offroading

Just expect the trimming and you should be fine. Getting the proper wheel spec will be key on how much you rub. The wheels I have are 16x8, 4.5BS and 0 offset. Hope that helps.
Here's some good references:
http://yotatech.com/showthread.php?t=44027&highlight=trimming
http://yotatech.com/showpost.php?p=363719&postcount=7
http://yotatech.com/showpost.php?p=363721&postcount=9
http://yotatech.com/showpost.php?p=363722&postcount=10
Good luck!