I've found that these can be tight too. One of my posts has a picture of how I did it.
You mention a wrench. I use a 19mm 1/2" drive six-point socket with a breaker bar, and remove the half-round plug in the end of the head to allow access this way. On the camshaft I use a 10" Crescent wrench on the rough hex at the center of the camshaft, and support the end with a 2x4 against the floor. That's with the engine on a stand, though. I see that your engine is still in the van so the crescent wrench can be supported against the body work to keep it from turning.
I hope there's enough meat on the bolt for a six-point socket to get a good purchase on it. Otherwise things get much uglier.