well im replacing the head, ive heard that u should always get it decked...and some say i dont..i was wondering how i would know weither i do or not...of if there is even a question about it

 

there is something called a feeler gauge, and basically u read the specifications on clearance for the block, and put a straight edge across the block in all lines of symmetry. Stick the proper size of the feeler gauge under and check 4 clearance, if it is more or less than specification then it needs to be decked.