key signature for orchestral score

Hello,
I'm actually working on a score from John Williams (Jurassic Park).
The score is written without any key signature. Even the transpositing instruments have no sharps on their key signatures.
When having a look a the score, all the B and E are flat, so we must be in Bb major.
But in fact, all the flats and sharps are written along the score. Not on the key signature.
I thought it was written in concert pitch, but I was wrong since the transpositing instruments (Bb clarinets, F Horns, Bb trumpets) are transposed.
So when there's a note on the F horn staff, it plays a fifth below. But there is no F# on the F horn Key signature, so if the written note is a F, it must be read as a natural F (and a C will be listened). If I want a F#, I must had a sharp.

See below the very first measures of that score as it is written :

In Musescore, I'll have to write :

You see that I have to add naturals to my F to make them sound Bb and not B.
How can I do that in musescore ?

If I want to make a mockup of this score, I'll have to transpose on the fly. Good exercise, but... 22 pages. It's pretty tough !