If you alter the suspension you aim to increase travel on both the compression and the rebound stroke. Increasing compression travel effectively moves the wheel further up into the arch, if this is combined with fitting larger tyres you can run into clearance issues.
So if you fit +2" shock mounts on your wheel will move 2" further up into the arch (assuming the spring doesn't become coilbound beforehand). If your tyres also are 2" (for eg) bigger then your looking at 4" in total. I'm not sure how much space you have from standard though - as I've yet to measure up or find the info on here anywhere.