I 100% belive that all the music on the show, is original. Now, i can understand if certain songs were homages from others. But as for originality, it has it all as far as im concerned.
Of course, there are a few anime out there that borrow song themes from movies/etc. One off the top of my head is the original Bubblegum Crisis, one of the BGM is basicly a homage from the opening bgm to Blade Runner, and another Knight Sabers song comes from an intro to a song on the "Streets of Fire" soundtrack.
I just thought of someone to play Jet, Kurt Russel. Now, hear me out. He fits the physiqe of Jet, and he could have a shaved head and grow a beard. Accually, he would look pretty bad 'a being Jet, like Snake Plissken and Jet did a fusion. I just thought of that just now.
Well, i am a huge Kurt Russel fan, so that can be clouding my judgement. But hey, at least i got a name out there...