I'll take a shot if no else will:

Vintage Air I think makes a self contained evap/heater box that is compact and fits under most dashes but it works really well. They call it the Hurricane I believe. It is cable operated I believe so you could adapt the factory controls to work the box. The ducts are just ducts so they could be routed accordingly.

My info my not be exact but it is worth looking into. I only know this cause my brother is a Vintage Air dealer in his shop and has put in a many of them.