I'm not looking to build an old frame with all new components - I want the whole thing - drivetrain, wheels, I already even bought brand new first gen. Micheling Pro Race tires
after seeing few of that sort of bikes I must say they haven't received the treatment they deserve - the frames alone are mostly OK, just some scratches here and there, but what the components reveal - lots of dirt, dried grease, even signs of rust or corrosion - don't promise anything good. and that's without looking into BB area or headset... anyway most of those bikes were probably bought as cheap bikes and treated that way. it's really sad to look at, esp. since it's often not the question of mileage but basic negligence - how hard is it to clean your bike even once a season
That just part and parcel of buying an older bike. A threaded BB costs stuff all to replace and most Shimano ones do just fine anyway. Headset bearings are cheap, or if they're cup and cone they probably just need a little love.
The biggest issue I've found with older race bikes is a lack of tyre clearance, especially on wider rims. On my Colnago Dream with 17mm internal rims, 23mm tyres have adequate clearance, with 25mm there is probably 1mm clearance front and rear. Gearing is another thing to take into account if you live in a hilly area, Campagnolo weren't interested in compact cranks until around 2006, and Shimano only a little before that, so you'll learn to the love the 53-39 crank if you don't already.