Warranty/head questoins

I have a 2003 XG 350L, and the timing belt Idler pulley bolt broke and damaged the right side head (looking at the motor form the passenger side front tire). The motor has only 55K miles and I had the
timing belt replaced at 52K miles. Here the deal:


The dealer is going to replace ONLY the right side head.


All three pistons have marks on them when the piston hit the valves.


The Mechanic did a bore scope on the left side head and found no damage, its just odd to me, when the motor is running and I have all three pistons damaged on the right side, and the left side is good
condition.


My questions is:
If you replace one head should the other head have a valve job done to match the right side head, because the right side head will be brand
new, and the left side will have 55K miles on it. I am not happy with
this.


Also if the pistons have valve marks, why wont the dealership replace the pistons or even replace the block?


How can I negotiate to have the dealership replace both heads, isn't it common practice when you replace head you do both sides, where can I get this writing, as a defense to make this happen.


What about the pistons, I didn't purchase the car with damage pistons and its under warranty, how can I be sure that the rod and bearings aren't damage, Even a slight damage in the bearings could cause some problems in the future.


Finally, the rental car, should the dealership pay for the rental car?


What I need is written documentation to help me. Any information will be greatly appreciated.


BH