A 3 inch kit will allow you to run 31's, depending on the back spacing you have on the wheels. Many companies make a 3 inch, take your pick. With 3 inches and 31's, you may rub a little bit... but only minor trimming would be necessary. I have trimmed GC bumpers a few times If you want more details on how to trim it and make it look right, send me a PM.
The two inch spacers that you are speaking about...I assume to be coil spring spacers. They are often referred to as the "budget boost" or "budget lift." Daystar makes a set. There are others as well, I found mine on e-bay for less.
Placing the 1 3/4" coil spacers on top of a three inch lift gives the GC a great look. However, the spacer will completely cover the centering shaft type thing on the rear. I went to a muffler shop and had two pieces of pipe cut, then expanded one end. I slid them on and tacked them in place. This makes me feel much better...when wheeling, you don't want to flex and loose a spring. WIth a lift that high, make sure your track bars are properly re-located.
Too many details to cover, if you want more info, let me know. I can give you many details. With a 3 inch lift + 1 3/4 spacer, and minor trimming, I am running 32's with no rubbing.