like these guys said make a bracket like shown or i personally put a pry bar on a tooth of the flywheel and rest it upon one of the guide pins for the trans either way impact gun is your best bet if you still cant get it out put them back in and tighten them down pretty good as stated and try that and my last suggestion would be to use some kimball jackson pb blaster i had a stuck one on my last build and after spraying it down with that for a day and a half i finally got it to break lose nothings ever been too stuck for it you can find it here:

https://www.kimballmidwest.com/Catal...aspx?dn=80544c


hopefully that will work if it is your last result I would bet that it will come out with that!