The probelm here is the dissimilar metals of the studs / bolts to the
alumium heads.
Electrolosis is a pain to deal with, especially where it's difficult to
get to, as in the head exhaust flange area.

Heating up the engine won't relly help, as it's not rely getting white
hot.

I removed all 8 nut's , bolts, and studs, in 15 minutes, by just geting
them hot.

One look at them and I didn't even try to yank on them without heating
them up.

The rest of the exhaust bolts were done the same way, and I saved a
bunch of time, energy, aggravation, and new catch phrases that I
wouldn't want to repeat.      ~: )

Then after it was all said and done I went and bought a bottle of 2500
degree anti seize, and all stainless nuts, bolts, flatwasher's, and lock
washer's.
everthing got them on the bottom side of the Van.

This job will be easier the next time around .