For any loved ones or other supporters, apart from the finish line, the best place to catch your 70km runner in action is up the top of Mount Blackwood. On the way out, this is about 20kms along, which could be under 2 hours for the fast people or 3.5 hours or more at the other end. On the way back it's at around 43kms and hence, add another 2-4 hours to that time (get a steer from your runner on their expectations!). You can drive up to the summit of Tower Track where there is some parking. Runners don't go right to the summit but run over the crest of the steep grassy slope directly leading on from the end of Tower Track, before running down Tower Track (or after running up it, on the outbound route).
If you fancy a bit of a drive (at least 40 minutes each way), you can also catch 70km runners at the Swans Rd turnaround and aid station, about 35kms in to the run. Parking here is limited, but you can park on the edge of Swans Rd - please be considerate of locals and park your car as far off the road as possible.
Also, 2kms from the start/finish is a lovely river crossing at North Blackwood Rd, where you can park and see runners come through