With a recent campy derailleur you'll overshift by about 0.25mm on each click so it may work ok by playing a bit around. Pre-2001 8-9sp campy derailleurs come often on eBay and I think you still can get 8sp cassettes new (I know I could last year).

You can also try those jtek shifmate thingies and use some shimano derailleurs and cassette.

Edit: also you could replace only the (long) cage of your D by a short cage from a recent D.