Hello and Welcome to justanswer..
In that case.. with all that you have done...they are truly seized.
Given all that you have done so far- I wouldn't apply more brute torque for fear of breaking them - and worse still , taking the alloy threads out with the bolts..
What I would suggest is apply heat - a lot of heat..to the head of the bolts.... so that .. the heat goes down / travels down the bolt ...and hopefully helps to un seize them in the threads..
I say a "lot " of heat - you will need a lot - and you will need to judge it so that you get the bolts hot enough - so that the head of the bolts don't twist off....but the heat does its job in releasing the threads..
What I suggest - what I have found successful before - is to apply the heat....don't be tempted to rush it - blasting it with heat - but play the heat long enough - slow but sure - enough until the bolt head is red hot.... You then need to judge it so that the head of the bolt cools back to colour...so that you wont damage the bolt as mentioned above- but the heat will have by its very nature - travelled down the bolt (s)...and released the threads... so allow some time for that to happen before attempting removal.
Again - this does work.. but it does take judgment .
In extreme cases - if they just will not come out - you can get the bolt hot enough to take the heads off the bolts - then lift the head off out the way and then deal with the threads - where the bolts are seized. In such cases - welding a head back on the bolt - using heat more directly in the treads - and then removing them.
If you do all that as above ...and it doesn't work - you can confidently say that you have done all that is humanly and mechanically / technically possible .. and the only answer then would be a replacement engine - which does happen... I Sincerely XXXXX XXXXX have helped you - but do ask me if you need anything more..
Kind Rgds, MIKE
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