Dwain,
For one,the heater core sits in the box really tight, especially with the little rubber seal they give you. You may have to trim the heater door a little or a lot. But definatley trim until it moves easily.
Assembling the heater box is not the problem with the old system, although they are a pain, it's the Fan module that fits in the passangers footwell area. Now that is a real pain to put in and takes up valuable foot space.
The fan draws air in from the foot well area, forces it into the core and then out the vents. Beautifull set up really. Especially since the Vintage air type systmes hadn't been invented when CR's started shipping the Heat/Def. package.
Want a new style call me... $295.00 including shipping. We're a VA dealer.
DV