Just got a new old bike (1984 Trek road bike) with a 6 speed free-wheel. I'm upgrading to 700c wheels, want to put a 10 speed cassette on it. I have a new 10 spd chain and laying around an 8 spd derailleur. Bike has original downtube friction shifters. So once I have a 10 spd cassette, what else do I need... new derailleur (can i use the 8 spd)? new shifters?