You might find the project is not feasible.
A long time ago when I was a poor student, I had a cheap hybrid bike and became interested in cycling. I learned that good bikes intended for riding on the road as opposed to off-road come with high-performance narrow slick tires and a drop bar. High-performance narrow slick tires I could install to the hybrid bike, but drop bar would be a more difficult thing. Firstly, the brake levers and shifters need replacing with drop bar variants, and secondly, the hybrid frame geometry would not be ideal for installing drop bar (it even had a cheap suspension fork!).
I knew if I wanted a drop bar bike, it would probably be Surly Long Haul Trucker, but I didn't know if I wanted a drop bar bike (never having ridden one) and Surly LHT was out of my budget at that time.
Knowing that in the 1980's cheap drop bar road bikes were fashionable until they were replaced with the cheap mountain bike, I started to find if I can find some abandoned bike with frame size that would be roughly ideal for me and drop bar. The purpose was to ride it for a while to see if drop bar was my thing. I found one, not particularly good, and started to investigate what I had found.
I made the following observations:
- The barely functioning bottom bracket was of the Fauber style, not threaded, and installing a modern bottom bracket won't work because modern ones have a different attachment (threads)
- The cheap and heavy steel frame had 120mm or 126mm (I don't now remember which of these) spacing on the rear. Cold setting might work to allow installing a modern wider hub but would be a bit too much to invest into this junk frame because even if I could cold set it for modern spacing, there's still the Fauber bottom bracket problem. Using the existing wheels wouldn't be a good option as the single wall rims were marginal, some spokes were cut in half, spoke nipples didn't turn freely and the hub bearings were practically seized, plus also the old rear hub was a freewheel hub and not a cassette freehub
- The brakes were cheap center-pulls. Finding modern brakes to install might not be so easy (as the trend was as of this time that road bikes with room for no more than 23mm tires were fashionable, so finding long reach brakes would be problematic as nearly all offered brakes were short reach)
- The shifters were downtube friction shifters. I could replace them with modern bar-end shifters only if I could find 6-speed indexed bar-end shifters (I couldn't).
In the end, I decided to salvage whatever parts were useful from the abandoned bike. The only part I could ever find use for was the drop bar itself (fortunately, it had 25.4mm stem attachment and not 26.0mm stem attachment). I never rode even a kilometer with the abandoned bike, because it wasn't in such a condition that I could ride it.
So I modified my plans. I ordered 8-speed bar-end shifters from eBay (they weren't manufactured anymore so new-old-stock or used were my only options), V brake long pull drop bar brake levers from a German online bike part shop, and installed the drop bar to my hybrid bike.
I found drop bar was my thing. I enjoyed it greatly even though the hybrid bike frame was a bit too long for drop bar use. The bike I had was probably the strangest bike on this planet -- it had drop bar and cheap suspension fork on the same frame. Later, after finding employment, I assembled a Surly Long Haul Trucker from parts so that I had the bike I wanted to have. I found the LHT frame geometry was better than in the cheap hybrid bike for drop bar use.
My advice to you: if too much of the parts are very old and barely functioning, it might be more feasible to salvage any parts that you might consider using and throw away the rest. Then install the salvaged parts to some other bike.
Especially if the frame is of an old standard for bottom bracket or hub attachment, it might be very wise to salvage any parts you might consider using and throw away the rest.