flex/deform while maintaining faces/bodies

[MattBD]

I have a part (attached) that I am trying to bend. However, I am trying to bend it only where the through slot is, and nowhere else. I want the other faces to remain oriented as they are, and in the case of the partial slot, remain in their original position.

I feel like I'm close, but just missing something. I'm also not sure whether the flex or the deform tool is the right one for the job.

Thanks,
Matt