Unfortunately those inversion scramblers are a little more simplistic than today's state-of-the-art. Modern public safety radios are digital, so the signal path is more like:
voice -->a/d converter -->AES encryption -->frequency modulation of data (transmitter) -->demodulation of data (receiver) -->AES decryption --> d/a converter -->sound.
At the core of this is a data stream getting AES encryption so I suppose that part is as crackable as any other AES, but I think there is a long way to go to get there.
Have a look at GNU Radio. There are a few AES plugins for it, ex https://github.com/sbmueller/gr-openssl