I dont have that year but i have a 91 and i got 5 trumpets to mount. You might have to go behind the grille or on the side of a fender wall. Im putting mine between the oil filter and windshield washer reservoir. Then that way the compressor goes in place of the stock horn mine was next to the air intake hole and the wire for the horn is rite there. It takes some figuring to do.
http://istargazer.ca/mods_exterior_airhorn.htm
http://www.miata.net/garage/horn.htm
Im using those 2 websites as reference for me. I am assuming in your year the compartment is pretty tight, so some of those pictures might give you ideas.