pour penetrating oil on the seam of the mating surface or the 50/50 mix of acetone/atf - let it sit a few hours - re-apply oil. Also apply oil to bolt surface. I would do that for a day or 2. Then get a small steel mallet - and give a few good whacks...IMO Can you post some pictures of how the manifolds look?
...A bad day water skiing still beats a good day at work...1995 Pro Star 205....