While conversion cassettes and Jtek's Shiftmate work OK, they're not perfect. The best performance is achieved by using a genuine Campagnolo 8 sp rear derailleur and cassette. Others might disagree, but I've tried them all and on those early Campy bikes keeping it all Campy gives you the fewest headaches IMO.

If your spare parts box is all Shimano, I'd suggest selling the Campy brifters on ebay. Chorus and Record brifters, even in average condition, bring over a $100.

Tim