>>Actually, you answered your own question. The "SpeedMod" daughtercard was
made to increase difficulty and as a result eat up more quarters. It was
not
produced by Atari...
>>

Atari did make some. On the top of the board it has written:

RATE MULTIPLIER BD
A035885
ATARI (c) 80
made in USA

On the bottom it has:

035886
1 (in a box, denoting revision #)