I wrote the article in Miscellany about the CDC hydraulic system. I'd be happy to send you a copy if you PM me.
It can be fitted by a competent spanner juggler and I recommend it. I have just fitted a smaller steering wheel (14 inch wood rim Moto-Lita in place of the 15 inch leather one) and I'm more pleased than ever. It provides the right amount of 'heft' and balance and avoids the tendency to over steer (as opposed to over-steer) because of the assistance. The only other tweak has been the purchase of string-back leather driving gloves which provide a good grip on the wooden wheel but sadly don't make the car go faster (unlike the re-map and sports exhaust recently fitted by Williams)

There are electric systems but I have no experience of them except Morgan's version on a 3.7 Roadster. I recall I did like the assistance because my 2004 Roadster was always too heavy at low speeds but I was too hung up on the rev hang to notice much about the steering.
Drove across country last night and the whole car was just wonderful.
