In theory, if the original bolts have not been over-torqued they are infinitely reusable. We all know real life is a bit different than theory but I wouldn't hesitate to reuse a stock set of head bolts as long as they all came out without a struggle and are in good shape (not corroded, no damaged threads).
As steve25 says, run a thread cleaning tap down the holes in the block and you should be good to go. Here is what you need for that:
https://www.pegasusautoracing.com/pr...sp?RecID=24891
When reinstalling the old bolts, pay attention to how they feel when torquing them. if any of them feel "mushy" and take significantly more turns than others to come up to torque once they start tightening, then you probably want to replace them, but I'm betting they'll be fine.