Originally Posted by
Wogsterca
Surprisingly little has actually changed enough that a bike built in 1978 can't use modern components, the only exception might be some French and Italian bikes, that are older might have headset and bottom bracket incompatibility issues.
There are also wheel spacing issues to consider. Older bikes are often designed to have only 120mm or 125mm of space between the rear drop-outs. Modern road bikes and wheels are designed for 130mm. Similarly, spindles on older rear wheels may only be designed to accommodate 5- or 6-speed cassettes. Steel frames can often be spread to accept modern wheels, but it's easy to break the bike or screw-up the alignment if you don't know what you're doing. I don't know of anyone currently making 120 or 125mm hubs for road bikes, though I'll admit I haven't looked very hard.
Personally, I wouldn't want to deal with these issues and would only consider buying a used bike if it could accept modern 130mm wide 700c wheels and an 8-, 9-, or 10-speed cassette.