I want to use new head bolts on this rebuild. Is there a source? I'd like not to use studs and i am not sure how to ask a bolt vendor for the proper bolts. Someone told me grade 8. Other than that, what matters? Does the length of the shoulder have to be the same? In other words, instead of say, 2 inches of shoulder, what if it only had one inch but the bolt was the same length? Thanks in advance