Bolts or studs and why

Thanks to everyone for your input. This not my build so I did not know if any of the holes were wet or not. I do know the headers are held on with bolts and not studs. It was always my thought that the exhaust manifold or headers should be held on with studs. One my concerns with the bolts would be steel to aluminum seizing and breaking. I am getting ready to start a disassembly of the vehicle and want to make sure I have the correct pieces and parts befor going back together.

Bobby