I found this on eBay this afternoon.
http://www.ebay.com/itm/Apple-II-not-Plus-VERY-low-serial-number-2105-accessories-Mockingboard-/300884765945?pt=US_Vintage_Computers_Mainframes&hash=item460e212cf9#ht_9147wt_907
This person has mistakenly placed the Motherboard Number as the Serial Number.
I see no plate on the bottom of the case showing the serial number.
But my question is "2105" for a board number?
Is that possible? 
Steven
http://applefritter.com/content/rev-0-apple-ii-ebay
Bush,
This is not the same computer is it?
The Seller sent me an email with a picture showing Serial Number 1836.
Is that the Serial Number of the II you're bidding on???
From the pictures of the inside I'd swear this is a FrankenII
I wonder what the two user-drilled holes are in the baseplate? One seems to play host to a potentiometer and the other a push-button switch of a sorts.
Probably something to do with reset and volume control perhaps? Talk about devaluing a nice computer..!
To answer two questions about this computer... Btw. He has a link to like 40+ pics including the bottom serial number sticker.
Rev-0 boards were labeled with serial numbers. The serial numbers were higher than the actual machine numbers because Apple did sell boards only. My rev 0 serial number is about 700 less than the board number.
The mod does devalue it a little but I would think not much. It was a typical period correct one. We aren't talking about a serial # less than 200 here, there were a few thousand rev-0 machines. On my sol-20, there was a typical mod to cut a piece of metal from the cover so you can open the computer when it's on. I debated welding a new piece of metal in but since it was typical of the time I decided to leave it. Back then people modded their machines. It was the hobbiest period of computers.
Cheers,
Corey