The road maps for this area of Quebec are inconsistent, vague, and sometimes downright contradictory. The official topos are dated (1976) and can't be trusted for road info. While several maps, including the Quebec Canoe Camping Federation map, show the shuttle route as illustrated on the previous page, others show nothing of the sort. This route, however, does exist.
The few Quebec road maps indicating local route O-764 will give you a pretty good approximation of the route, but talk to local residents for accurate and current info -- roads wash out with some frequency. The Jim Lake route, however, does appears to be sound and stable, at least up to the Manitou Rd. (K115). It's the route that the logging companies currently depend on.
Which brings me to a final, cautionary note. Stay right and stay sharp! Those monster logging trucks always have the right of way. Better yet, stay off the roads between Monday morning and Friday at 11:00 am. Weekends are thankfully free of commercial traffic.