stuck open intake valves on slant six

I'd start out by pulling the valve springs on those two valves, using the rope method like you would do changing valve seals. Once the springs were off I'd try to spin them and work some penetrating oil into the guide. Maybe even chuck the valve stem in a drill and spin it that way, also opening and closing the valve at the same time. If you can get it freed up good enough, it might save you from pulling the head. I'd be tempted to check some of the other valves too, to see if they might be prone to seizing too. If you can't get the valves to move easily, it's pull the head time and get things done right. Hopefully, the valve(s) didn't get bent too. Good Luck!