Is installing a full exhaust system hard?
Is it just as simple as taking off the old and replacing it with the new one?
or is there calibrations and junk?

Techically you should rejet the carbs after installing a full system but installation really is a snap.

bolts right in simple. But wont run well unless you also replace the jets inside the carbs with bigger ones, depending on what else you do. That's the more complicated part. Full system helps top end at teh expense of low and mid range driveability, I've heard.