you don't want to sit on a worn out baler you don't want and you have had limited calls on, especially after it's missing a major drive component. It might be a hassle to get rid of it and even if you part it out, you'll still end up with the bulk of it in your way so it might just go to scrap.
I would offer him the whole works for the same price. Let him deal with taking it apart and dispersing of the excess pieces. Also if something important to the buyer breaks during disassembly in your yard, you may end up with no money and a junk engine and baler.
If you have multiple calls on it for pieces, maybe you can split the machine between buyers.
Depends on what you want and how you feel.