I did the exact same thing to my '80's Fuji Absolute (converted it to downtube shifters). I got a set of suntour racheting downtube shifters and clamped them on. I don't remember what the original derailleur was but there's a suntour V GT Luxe on it now, and it's great. sure, it's no where near a high end bike, but I love mine, and have put more miles on it than any bike i've ever owned. most comfortable bike i've ever ridden.