Replace Rusty Risers and Manifolds?

[51timber]

Looking for your thoughts. Are these risers and manifolds worth saving? I am thinking not, though I have seen a past thread where they were cleaned out once and looked pretty good. My Big concern is even if I replace the risers, I don't know if I can get the bolts off for the manifolds (SEE PIC).

Since the bolts are so rusted on the manifolds, can I cut off the heads of the bolts off and then pull the manifolds off then back the rest of the bolts out with Vise grips???

If I replace the manifolds do I need a sealant of some kind along with the gaskets?

Thanks for your advice.