if the stuf looks good and not waisted.. doube nut it.. and get hte old nut loose of possible.. then install and torque down. a micro smear of ptfe or similar paste won't hurt it.
on the manifold to block.. many have reported good results with some sort of steel filled epoxy applied with wax paper.. thena file / sand job.
I'd back that up with new gaskets and some hight temp red silly cone.. I don't normally use goops like that.. but there are a few cases it may be ok.. ideally, if the manifold was pitted.. you would resurface or repalce it. i realize thats not always a feasable option.