Dunno what the dash is like in the Poncho, but in my Olds there's a plastic woodgrain panel (see my avitar) that covers the factory radio. I bit the bullet and hacked it with a Dremmel tool to fit a new style radio. Took me a day 'cuz I was scared shitless of messing it up. Came out nice, and worth the hassle.
Of course if you're into showing the car or keeping it original, a CD player hidden in the glove box works too. Not real convenient though.
1999 Buick Park Ave Ultra
Head Unit: JVC KWHDR720
EQ: Audiocontrol EQL
Front Stage: Hybrid Audio Technologies Imagine 5.25 mids, Morel Maximo tweets
Sub Stage: Boston G3 10", 0.5 cu ft sealed
Amp: PPI Phantom 900.4
Rear Fill: Boston SE953 6X9's