1. No, stock IH style gasket works well with some Permatex Copper Spray on the gaskets.
2. Yes, be sure the mating surfaces of the exhaust manifold are flat. Also, when installing, check to see if all the attaching bolts
can be threaded into the head finger tight. I recommend a tap to clear the threads in the head first. If the bolts don't line up properly to the head, you may need to drill out an offending hole in the manifold just enough to allow the bolt to line up correctly, without any stress or strain.
These manifolds were only used in two model years ('74 & '75) so they can be scarce to locate. Be gentle. Use C-5A Never-Seize copper coating on the bolts and threads in the heads.
3. Maybe, depending on the condition of your manifolds.
4. No.
5. No.