Model M International grain drill

I have what I think is a model M International / McCormick grain drill. One of the 8 tooth clutch sprockets to engage the drill is worn down so bad that it won't stay engaged. That part is not available anymore, but I believe I could rebuild it with some intricate welding and grinding. The problem is, I don't know how to get it apart. I was hoping that someone would have an exploded diagram to look at.

 

Thanks,

 

Paul N

Model M International grain drill