Thanks again for all of your comments. I am getting extremely educated on this subject and I appreciate it.
In response to Ryan, yes, there are constraints for the air handler in the width direction, not height. This may be the reason why the Carrier proposal came back w/ that particular air handler.
And also, for the TAM4, I was quote for the XB series, not XR. So no variable there though I think I'd like to have a variable speed air handler.
Thanks for the EDD comments, will take note.