Dear Dave,  Greetings from The Bronx.  What your rocker type lever
may be is a "Pause-Accelerando" Lever.  I've only seen this in a few
88-note players.  The rocker lever is balanced by leaf spring or
springs, to remain level until depressed for the required effect.

Depressing the "Pause" end enables a cut-out that stops the rotation
of the roll motor, while depressing the "Accelerando" end, enables a
roll motor governor by-pass, causing the motor to speed up.  Releasing
the "Teeter-Totter" type lever allows the leaf spring or springs to
center, thus allowing the roll motor to resume at its previously set
tempo.  Hope this helps,

Sincerely,
Dale F. Rowe
Bronx, New York