Looks like you've got a nice original machine, with the correct tokens no less (which are often missing).
I've attached a photo of the same side below for comparison.
Here's what i see in your photo.
I think i know what slotted piece you refer to, but there are at least 4 slotted pieces in your photo.
The upper most slotted piece is the main coin chute.
For discussion, let's say the coin chute is two halves;
the inner half is attached to the mechanism side frame.
the outer half screws onto the inner half.
The coin chute makes a turn at the rear and goes straight down
The bottom part of your outer half coin chute is broken off.
If you remove the reject coin deflector (2 screws where the coin chute angles downward), you will see the break.
That slot at the bottom of the coin chute is in the inner half of the coin chute and would not be visible if the outer half were not broken.
On the bottom of the outer half should be a lever (missing) that holds the coin in place until it is ejected out the back into the coin chute attached to the back door.
Just below the coin chute is a sliding arm attached by a slot that slides along the screw holding it in place.
Your sliding arm is installed backwards; it needs to be flipped over.
The pin at the center of the sliding arm goes into the slot at the end of the "V" lever at the 12 o'clock position.
The end of the sliding arm goes into the bottom of the coin chute; between the inner half and the portion of the outer half that is broken off your coin chute.
The sliding arm pushes the coin backward into the coin chute attached to the back door.
On the left side of the photo, there is a round operating lever with a tab.
In your photo, the tab is at the 8 o'clock position.
When the mech is at rest, it should be at the 10:30 position.
It cannot be seen in either photo, but there should be a spring attached to the pin on back of the round lever that pulls it up to 10:30 position when the handle is released.
Interesting note:
I see there is a spring on your round lever that is attached to the small lever mounted on the round lever.
My machine does not have that spring and seems to work fine without it.
I don't know the purpose of the spring, but tried to fit one on my machine; there was not enough clearance on the machine between the round lever and the side frame to attach a spring without binding.