I want to swap heads, on my 95 to my 96, the 95 just had a valve job, do I need to change the head bolts? If I do, why?

 

Head bolts stretch when torqued. rule of thumb you should change them every time the head is removed. but, spud stated before they are designed to be used a second time; after the second time they should be replaced. Same is true with the connecting rod bolts; but they can ONLY be used once.