Regarding the Pratt Read air motor, it is true that the moveable
boards of the pneumatics are not hinged in the conventional manner.
The pneumatics should be recovered with a one-inch "span" of cloth
across the boards on what would normally be the hinged end of each
pneumatic.  This then will allow the moveable board of each pneumatic
enough upward mobility to be properly screwed to the underside of the
thin board that joins each pair of opposing pneumatics and the motor
will operate properly without binding.

Try to dry fit each pair of opposing pneumatics with their associated
teeter-board and mark the most advantageous positions for alignment
before gluing.  If alignment after gluing should turn out to be less
than ideal you can always plug and re-drill screw holes in one of a pair
of opposing pneumatics and make any needed corrections that way.  Hope
this will be of help.

Lance Reed - Resurrection Piano Service
Johnsonville, New York