I have a 1986 Isuzu i mark and there's no speakers in the back just up front. I have the wires for the speakers and the cut out spots in the trunk for them so i could install them...but the problem is i don't know what size of speakers to put in the car....i measured the hole for the speaker like from one side to the other is 4.5" so what size speaker could i put in it? and what brand?