If your machine is an S+...>>>
Turn it on, let it boot up, and press the little white test button.
The little white test button can be in three places on an S+.
The front bottom left of the power switch, behind it, or on the MPU enclosure itself.
Now, press the test button ten times or until you see a number "4" in the [Coins Played] window on the display.
Look on the left on the display panel at the [Winner Paid] window and you should see a four digit number flashing there.
Some chips make it alternate instead of flashing.
That is the number of your REEL eprom.
The number in the [Credits] display is the GAME eprom.