Interesting pickle, my only experience with stuck aluminum head was the aluminum and studs corroded, in that case we tried compression which didn’t work and ended up filling a cylinder with trans fluid to create a hydraulic lock and turned the crank by hand.
How are you getting purchase to pull on the head? Through the spark plug holes?
If one side is already loose then it seems there is a start at peeling. I am guessing that the bond holding things is primarily the turned copper flanges of the gasket at each hole since most of the gasket would pull apart away from the holes.
I am wondering about threading some rod into each spark plug hole, drill holes in a 4 × 4 wood to match with bolts above to get as even a load distribution as feasable. The spark plug holes in aluminum of course aren’t the strongest, although if you strip one out you can probably repair.
With one side loose already, the off center of the spark plug holes should provide some peel load instead of straight tension. I would load it up and let it sit awhile with the hoist loading it, and increase the load day by day to try and mimimize the risk of breaking the head before it lets go.
You may have already done this to get this far. Actually, I am amazed you got the studs out first!