Brett - have I got the answer for you. I spent about 3 weeks researching this issue. As a musician and audio enthusiast I have access to a lot of data of speakers. I searched the net, catalogs and stereo shops looking for a heavy duty speaker for this application. The factory speaker and sheet metal depressions are not - I repeat ARE NOT - standard. The factory (Hatachi) speaker is a non standard 4.6 inches (some kind of metric thing no doubt). A 5 1/4" speaker will not fit unless you want to butcher your car. I'll save you (and me) a lot of time and cut to the chase - go to RADIO SHACK (don't laugh) and buy P/N 40-1284 this is a really decent 5" (odd size) speaker with a 10oz magnet (about as big as will fit in the depth avaliable) and a wizzer cone. You will have to grind the speaker frame a little to get it to fit the depression (get out your bench or hand grinder). The bolt holes line up fine. One last thing - put some fiberglass insulation in the cavity behind the speaker and run a bead of silicone around the speaker opening before mounting the speaker (damps the sheet metal and reduces any resonance/buzz).