You can get that open by using penetrating oil (think Liquid Wrench, Kroil, etc). Spray the shafts (in and out). Let it sit a while and then gently tap with a small hammer until you feel it start to move when you wiggle the counterweight. Or at least that's how I usually do it. Some claim you can heat the manifold up, quench it and that will free it, but that trick never worked for me. But I figure somebody will show up in 10, 9, 8, 7, 6 seconds and tell you to do something else. In my opinion you mostly want to let the penetrating oil do the work, wiggling a bit to help it along. It may take a while, however it took a while for it to get in this condition...Good luck! Years ago there was a penetrating oil made here in Texas that was a real treat to use and would free something like that up in a minute or two but the company closed.
