I would definitely try metric screws. The part number definitely is in the JBL system as an 8-32 but I wouldn't put it past them to get it wrong on the drawing. Remember the M2 crossover shows a wrong value on a capacitor. Things happen, people make mistakes. It isn't like most flown equipment doesn't use metric hardware rigging. It isn't like metric isn't in the JBL plants already.

I'd be flabbergasted if it was an obscure size like 8-36. It isn't until we get to #10 hardware that one sees UNC and UNF stuff. An Altec, they liked using 3/8 UNC AND UNF on the same stud for mounting the 288 and like drivers.