I think the large metal bracket is to hold the knee lever. There were two types, one latched inside using the handle bolts, the other was held in by brackets on the side - yours looks like the side type.
Here is a picture showing the oil case in place. This is a lid for a handcrank machine, so no brackets for the lever.
Yours looks like it had a lever at one point, and someone may have changed it for a foot pedal.
I got mine without the dome, and the wires cut off. At least the control was still there and usable. Then I found a second machine with a busted bottom case and a nice top, and then I bought the WRONG knee lever (had no idea there were two) and then I bought the right one, and then I discovered I needed a third style to use with the cabinet . . .
(DISCLAMINER - DH and I have rewired our entire house 135 year old house - from the lines coming in on. We had the power company hook it to the pole, but that was it. So we are familiar with wiring).
Anyway, here is the cord DH put together. He "color coded" it because it is a polarized plug. He used the original ends. We had them from a different machine that was wired into a cabinet.
This is the machine end - does yours have the hole in the plate? DH also color coded the connections here to keep the polarity correct for the control and motor.
This is all new wires - he opened up both the light and motor to do this. He bought about 25' of some wire to use for my machines, as we aren't into "vintage" electrical. Worn cords are replaced.
Here is the insides. I thought the control was rusted - DH said that is a normal coating.
This is the girl - She'd spent the previous 5 years in an old Quonset hut in MN (no climate control, dirt floor) - and before that had been with a bunch of stuff removed from some Junk shop when the owner died (uncle of the current owner). umm- anyone need a buttonholer?
With ours, both the light and motor are connected to the wiring, though the motor is connected so that the hot feeds through the control, the light is directly to the incoming wires.
I have a motor with the same outlet/foot pedal your picture shows - this is where DH got the ends to use on the replacment cord.
You could replace all the cords there and keep using that style - or you could put the wiring block on the back and use a newer style cord. I have those two if you want pictures.
I've ended up with a variety because I was going ofter machines from different years - and cabinets so I've ended up with a lot of different motor/light/foot pedal combinations.