New muffler

I have an 03' Mustang V6 base model. I want to replaced just the stock muffler with a flowmaster 40 series delta. A couple questions. First, has anyone replaced just the muffler and if so, did it sound really nice. Were you wowed by the new sound? Also, do you know what the inlet and outlet size of the stock pipes are so that I can match the correct flowmaster? Thank you.