You took the coin-in optics apart but didn't show us a picture of the black plastic encoder guide?

There is no model number that will tell you what it was.
It may have also changed during its service life.

Coin in is based on coin head. (External metal entry).
Coin comparitor cc-16 or cc-33.
The 16 is for small denominations up to a 1/2 dollar.
The 33 is for large denominations from $1 up to $100 tokens.
Both work the same way and are interchangeable.
They compare the metal content in the sample coin with what is dropped in.
I run mine off tokens that are in similar size to a quarter.
Next is the ABC optics it’s the small board below the comparitor.
This makes sure the coin is falling at the right speed and the right direction to prevent cheating.
The optic board has a spacer guide that makes sure the coin is sensed right.
Lastly there is the hopper. It would have a wheel in it to be able to eject a certain size of coin. As that is missing

You can set up the machine for the denomination of your choice.

Generally speaking if you had a cc-33 in the machine it’s likely a dollar slot or possibly a high denomination token. The latter being quite rare.

So take a Susan B coin and pass it through the coin head - if it passes your 98% sure it was a dollar slot.

The matching spacer in the optic is your final 2% assurance if that means anything.