I haven't done it yet, but I drive this road often. After Princhester Hut you walk through what is basically a farm, then hit SH94 and follow the highway until the turnoff to Mavora Lakes. From that turnoff to the Kiwi Burn carpark it's all gravel road — in summer it's dry and moderately busy as Mavora campsite gets very popular.
If you can i recommend you grab a ride through this section. The dust from passing vehicles makes it a bit ordinary and it's not exactly scenic walking along a gravel road. Once you hit the Kiwi Burn carpark you pop back into the bush and it's all good from there.