Okay...follow-up. Went to the dealer today...when I walked in the door they said the ExMark distributor had not gotten back in touch with them yet. I followed your advice and told them that I didn't want the mower...that I wanted my money back. With only a little bitching, i.e., "After all the trouble I went to"...I got it back. I did mention to them that if they'd called me when it came in they wouldn't have had to have installed the mulching kit.
Drove over to the other ExMark dealer and bought their Quest SP...like new. It will be delivered tomorrow morning.
Celebrated with a Starbucks coffee on the way home.