I'll have to grab a pic of the underside next time I see it - currently the old man is driving the car. I'll definitely grab a pic for reference though, but I could have sworn the catback ran down the right side of the car.
I don't have DHP (yet?) but I did confirm that there are files for the LeSabre. I'm assuming that, using DHP, it would be a matter of copying and pasting over supercharger files (throttle position, boost, MAP, etc.).
As an alternative, I wonder if HP Tuners might be a way to go forward?
For what it's worth the instrument cluster on the later model LeSabres are just like almost any other GM car (it greatly resembles the Regal dash except this particular car doesn't have a tach). Unless we're talking past each other somehow? Let me know.