Hi Chris
1. It is possible to ride from Beaverlac to Citrusdal, and folk have done it, but last time I checked you had to know someone to get permission as the roads at the head of the valley are strictly private.
2. Nature Conservation does not allow bikes in the Wilderness area. Biedouw Valley, the Postal Route, Wupperthal to Oasis and Clanwilliam, Algeria, Oasis are all public roads (mostly) and you can ride them at will.
I haven't been up that area much in the last 5 years and things might have changed.