I'll stir the pot by saying this :
you haven't lived until you've ridden a sub-20 lbs 1970's machine !! The ride is either great or terrifying !!!
I recently built a period correct 'light bike' based on a 1977 531 frameset and no Italian parts. I followed a strict discipline with a spreadsheet : cheapest grams saved first. And, I only bid on parts if they would reduce the weight of the bike affordably. In the end, i paid through the nose for one or two parts to get some premium titanium 1970's stuff from asian makers.
The bike is fun to ride and durable so far, and i enjoy letting others heft it before or after a club ride. Their reaction is typically, 'HOLY CRAP !!!' which is amusing to see ...
And I don't even have the microlite freewheel installed, nor the (modern) Ti square-taper bottom bracket ... yet.
- Don Gillies
San Diego, CA, USA