I just checked the measurement on the Bianchi. The top tube is the same length as my other drop bar bikes--54cm. However, the seat tube is much about 6cm shorter. But I think if I put drop bars on the reach is quite close.

I want to do as little as possible with this bike, keeping as much of the original equipment as possible. It currently has a 6-speed freewheel, 130mm OLD, twist shifters.

What are my options?