10,000 thanks for this. This is what we've always wondered about. Do you have any idea how long the "music director" had to do the cut-and-pasting? Days? Weeks? Months?
We can envision these folks keeping a notebook of "fight scene," "suspense," "diabolical chase," and whatnot so that they could cobble these together pretty quickly. But it would still be a huge job.
And...did the studios have copyists to write out the parts for the orchestra musicians?
It would be SO interesting to get interviews with these people.