Crutchfield.com will find what fits your car, but they won't tell you what the exact dimensions are. Pretty good selection but some good brand names are missing from their inventory.

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'98 SVT
KKM
TH fix
Upgraded stereo

'98 SVT
KKM / TH fix / Mobil 1 / Synth tranny cocktail / JVC LX-30 HU / 10" JL sub / Alpine V12 amp / Panther 199 wheels / Kuhmo Ecsta 215/45/17 / Bosch +4 / Ford Motorsport wires