I'm an MN modeler with quite a few of these cars myself, but I don't know of anyone who makes interiors.
With the tinted "glazing" on these cars, I'm not sure how visible an interior would be anyway...?
I will tell you this, though. I saw a superdetailed MBTA comet coach on display at a table in Springfield (Not for sale) and I was blown away. The guy did everything...and I mean EVERYTHING. There were painted/colored MU stanchions, lift rings, handrails, MV lenses, weathering, IHP trucks, diaphragms, silver stepwells, step plates under the doors...the works. If you really want to make these cars stand out, super detail them!
I've successfully put a DCC decoder in my CDOT cab car to drive reversing/controllable headlights and taillights, and it looks great! Now, I'm adding decoders and super detailing beyond just the brass air horns on all my cab cars now...