I've only ever driven up Porlock Hill. Always returned via another route.
First time in the 80's, on the R100RT, as part of a Bike Aid run - JoGLe (or leJog backwards...

).
Next time was in RiTA, a couple of months after buying her - Sue and I spent a week just outside Camelford...
Not done the Exe valley, but do know Dunster...
Will be around Exmoor later in the year, planned to be in the 90 though...