So many ways to go with this, but one thing needing clarification is the rear hub - what is it exactly? Even if it is newer, you're still running 6 speed with the a-3000, correct? If it is a freewheel, you don't want to go bigger than 7 speed. Even if it is a cassette, it probably won't go past 7 speed.

If you really love the steel bike, you could find some mid-90's aluminum bike (who likes aluminum anyway?) with functioning STI parts, strip it and transfer it all over. $250-ish dollars later and you could have a new drive train including wheels. Sell the frame for $50 and call it a day.