Have to agree with this. the dowels are not to hold the head in place they are to locate the gasket properly while the head is being replaced. So replace plastic with plastic and steel with steel.3 x bad advice IMO ...eventually explain why would you do such things but with technical arguments if you can not that somebody said it's OK
You reuse the headbolts at your own risk. For the cost, no, don't do it.
And why fit a thicker gasket? you can lightly skim the head and if it is only a tiny bit out it'll pull stright under the tension of the bolts.
The above from the great James Martin, (except that he does have a tendency to reuse bolts but then he is more of an engineer than a lot of us and knows exactly when you can and when you can't.
Don't change the engine just the oily bits.