So I have a question with regards to me taking out my old cylinder head unit and replacing with a new functional one. From my reading I am seeing that the head bolts will need to be replaced, is that because they have been stretched?
It is a general rule to replace them after replacement of head. But I have heard of people reusing head studs. If it were up to me I would simply buy new ones.
Dude, you do not want to be re-using head studs. You will have gasket issues if you do. The studs stretch after a while and you need to change them with the new head so that you have a tight, perfect seal.
Actually, there is a service limit on the studs. If you have access to a dial caliper you can check them to make sure they are within the service limit. I've changed out my head a lot and I've never seen the studs stretch beyond the service limit.