I tore my 58 Duplex apart after I found a nest like that. But, it still had a kangaroo mouse and its 2 babies living in it.
I've found 9 total so far, on of which had a snake skeleton and 2 mice mummies in it. I'm still finding them as I go along. I would recommend checking in the rear fender compartment near the tail lights, maybe the headliner and behind the dash. I even found one in the fuel tank! There was no gas cap so I assume that's how it got in there...