I haven't commented yet cos I've been playing with Rusty and his new hand crank.
Here is what I would try were I in your situation.
Since you have the new box get a piece of solid steel, "L" shaped, and cut it wide enough to be a strong support, but not wide enough to get in the way. Bolt it to the bottom and to the divider for stability. Bend it so that it runs right up next to the pillar of the machine with a tab at the top bent to keep it from bending inwards. Put a rubber cushion on that.
Drill a hole where the HC mounting bolt needs to be, then drill a smaller one above and below the mounting bolt hole to mount a small bolt or screw in to prevent the HC from pivoting. This is a substitute for the boss that's missing on your machine. Bolt the HC on and crank away.
Harder to describe than to do it.