Kwanten will play Manson in the film, which Kosar is adapting from his own script. The actor previously admitted that the role will be a challenge.
Asked about playing a real-life person, Kwanten told Metro: "I've done it before but it's like anything in life - you have to prepare and do your research.
"With Manson there's so much to read and only so much one person can absorb but ultimately it comes down to me and the director to present our interpretation of him."
Kwanted added that the project is currently "on the back burner", explaining: "I'm doing another film before it so hopefully we'll be doing the Manson film next year."
Lindsay Lohan has been tipped to play Manson family victim Sharon Tate, the wife of director Roman Polanski, in a separate Manson family biopic.