Sometimes even Easy-outs fail ... I prefer the stronger square type that you tap into the drilled hole in the bolt/stud rather than the reverse flute ones which can snap off easily (the small sized ones) ...
IF you use the heat method ... heat the stud bosses on the alloy head while trying to avoid heating the actual stud ... You want the alloy of the head to expand and let go of its' grip on the steel stud ... if you heat the stud it'll expand and get even TIGHTER in the head ...
With alloy heads , it's best to let a stud cool thoroughly before attempting to unscrew it ... otherwise it can seize onto the alloy threads and strip 'em out ... Spray WD-40 on the studs after you heat them to help work the lubricant in ...
IF you have stud sticking out that you can grip with vice grips ... you can heat the engine and head up until it's hot by running it ... then use a good long blast of cold aerosol spray on each stud to shrink it seconds before attempting to unscrew it ... There's Loctite "Freeze and Release" ... but good old WD-40 in a spray can OR even a can of under arm BO spray might also work ... Maybe you could put the can in a freezer to help cool it first ... (Poor man's Freeze & Release ...

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Welcome to: Loctite® Freeze & Release
Chinese studs are relatively soft and easy to drill ... For them to snap off in a new head while being unscrewed , they must be locked in there pretty tight ...
I've had studs snap off flush on a '74 XL350 head and they were so damned hard that a high speed steel drill bit couldn't even mark 'em ... I had to spot a nut onto the end of each stud with a MIG welder ... then heat the alloy stud bosses with a blow torch to get them out ... It worked great ...
Sometimes they'll come out with just a nut welded to the end because the heat breaks the thread lock ie red loctite or whatever was holding them in tight ...