I tracked down the map: this October 1979 Ministry of the Environment recreational map showing existing trails and facilities shows the connector from the Deeks-Windsor Meadows to Phyllis-Marion Lakes.
Note that one could now continue more efficiently further northward via the now-dominant trail to Capilano Mountain, via Beth Lake (not shown).
Great stuff! Thank you! (only 39 years ago...how badly overgrown could it be? ha ha)
I really want to try this now. Better get back in shape...