I know its a Skyline but this is a general CAT question.....

Just got my second hand HKS downpipes (fook they big compared to the std ones...no wonder they say you get a big difference!!!!!) and a de cat pipe ....now can i do this job myself??????I ask cause i heard the CAT is highly poisonous and is best left to a proper exhaust place.....now i know youd all like to see me dead but can i have an honest answer please...ROFL.