I had this issue when we installed the last KA. Try using a two breaker bars. One tightening a bolt (a.k.a, holding the fly in place) while loosening the stuck bolt with the other breaker bar. After that, hope the bolt you were using for leverage comes out easy, lol.
I've also seen people use a breaker bar on the crank pulley bolt to keep the flywheel from spinning, but I'm not sure if that's healthy or not. Use steady pressure with the breaker and you should get it.
I'd recommend using a flywheel/flexplate holder. It'll hold the fly or flex by the outer ring gear so you don't damage anything. All the methods mentioned before work but again it can be kind of skeptical.
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