The ACA does provide details of the trip itinerary on their website. Although it does not reveal the specific roads it does list the overnight locations. With a state map it's easy to find these and connect the dots between them. Click on "itinerary"..........
Portland-Crater Lake Loop | Guided Tours | Adventure Cycling Association
OP-
I concluded a trip (at least 25 years ago) from San Francisco to Eugene via Crater Lake taking Rte 97/58 for the last leg into Eugene. I don't recall any problems. I rode Rte 62 north from Medford to get to Crater Lake. That was real nice.