some pro peleton riders in the 90/s did ride with the ergo cables bulging under the handle bar tape, personally i dont like the look although dis comfort is prob negligable.
Some <one?> also used a right sti shifter left brake lever and left down tube shifter probably in an effort to shave off gram/s in the mountain stages.This i will do one day , well where i live the 42 is used much less and its much cheaper to buy an odd half pair at a cycle jumble or on line.
ive never really checked up on quill stem lengths down into the headset, i suppose the thing to use is a head set with a reasonably standard stack height .
stems,bars, seat posts < whether original era or retro /modern> can be the cheapest stuff of the lot!
once i have the year of my next frame, then the thing for me to do is find what group and components
came out about then,wheel rims,number of spoke holes,headset,bars, everything. nos would be nice , but i cant see it in my bank balance somehow!
buying a doner bike and transfering the bits is by far the best way i agree. If there/s one or two bits your not happy with i would keep them, bide your time then flog them and replace with what you want