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I also observe (when everything is connected) 0.7 Vd.c. at pin 3 relative to pin 4 when the motor is running and 0.2 Vd.c. when the motor switch is turned to off. This doesn't agree with the voltages marked on the circuit as it states 14Vd.c. 'at projection'.
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That's good as far as the output transistor is concerned. There is some drop across it, as though it is being driven on hard, rather than completely shorted. With the motor off there's no collector supply. The 14V is probably an average as measured with an analogue meter, when the output is actively controlling the motor voltage. If the supply is 40V and 14V appears across the output transistor, this suggests a typical 26V required at normal speed and torque.
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Is it linked mechanically to the one motor?
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Yes. Most 16mm projectors use a single motor, with a slipping clutch or other slippable coupling for the takeup (and supply, when reverse projection is available) that tries to drive it faster than the smallest spool centre requires. A standard mechanism on B&H projectors is a weight-controlled slipping belt. The takeup spindle drive pulley 'hangs' in a fabric belt, so that the increasing film load increases the friction on the pulley and hence the torque. Even some full size cinema projectors up to 70mm use a slipping clutch for the takeup, while others use a separate torque-motor with variable torque.