Thanks to everyone for your help.
The Trane dealer came by today and seemed much more knowledgeable and was a lot more thorough.
He's p repairing the load calc (the other guy said he was doing one but only collected about 25% of the data that the Trane dealer did).
He's also going to propose an attic install as an option, being a ranch with high ceilings he said that they can get great performance since they can design the duct work specifically for cooling the house and place all of the registers and returns high up in the rooms.
I'm not sure if the attic idea is a good one but it sounds reasonable.