Much like the way KLH used their single-driver table radio speaker in the Model 5's as a midrange, Bose has used the later-model 901 driver for a number of applications and with different impedances. You'll also find the basic driver and basket used in many automobile audio applications where you find the Bose brand as well as in smaller speakers like the 141. You should consider them full-range drivers rather than a woofer, however. All of these applications, however, use active (in the case of the auto or 901 application) or passive (in the case of the 141) equalization to achieve the desired frequency response within the limitations of the cabinet.
Your Series II's, however, did not find Bose doing similar tactics since their product line in the early 70s was not that large.
Cheers,