I'd probably be thinking 90s. Keep in mind that Brifters, indexed and tandems are a good thing. The 80s bikes from the folks previously mentioned are probably fine, but I'd also probably upgrade drive trains. There's a lot more cable with a tandem - friction shifting can be a pita. I really like having an eccentric bb on mine and would recommend them.

I am very spoiled by mine (thanks Tom!) and might be too picky.