Hulme was the chief of the GPDA 1975. At the race in Montjuich 1975 he was vacant, because he was wanted by the spanish police (with a warrant of arrest). Does anyone here know why?

Well, this is just a guess, but it might make some sense. Hulme was involved in an accident at Jarama the previous year, when, just after Brambilla going out at the end of the straight, some marshalls tried to help, one of them, crossing the track from the right (where the marshalling post was) was hit by Hulme. The marshall died as a result of the accident and, according to spanish law at the time (1974) of course Hulme was to appear before the court.
Remember, similar clashes of jurisdictions had happened in Italy, where, their legal system being very similar to ours (Spanish) it was not yet the time when accidents in racing tracks with fatal results were to be "ignored" by the judicial environment.
So maybe that was the reason why Hulme decided not to come to Spain in 1975. With Franco still alive, I fully understand that he might not have felt exactly at ease to have to present himself in front of a judge.

Regards
Felix Muelas

I've found this fact in an Autosprint magazine article.
The unfortunate marshal died some days after the accident at hospital.

Do you know why Denny Hulme drove a Texaco-Marlboro McLaren M23 with #56, and not #6, that day?

It was the Texaco Marlboro McLaren spare car, and as their regular numbers were 5 & 6, it was numbered 56, and Denny preferred this to his regular chassis.

/Conny