Stainless muffler question (for my friend)

My friend is an owner of a Chrysler van. He does not have usenet access (don't ask). Any help will be gratefully appreciated.
Dodge Caravan exhaust, muffler question.
Two ears ago I was debating whether to install a stainless muffler on my van. I was afraid to install something which will affect engine performance or potentially cause some engine damage through valve overheating or affecting the sensors in the exhaust line. In the end I bought the most expensive Mopar muffler with resonator, and I predicted back then that thy will not last for two years. They are rusted through now.
My doubts are the same.
Is it o.k. to install something different? I found a stainless muffler, it says that it should work for Plymouth grand voyager (this is what I have). !&modelidH3&year95&partid%&brandid$18
My questions are:
It doesn't have the same shape, could it also be rated for a different engine? How accurate the online stores are about their recommendations?
If I don't use the resonator, will that affect anything?
I will appreciate any advice. Thanks a lot.

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