Geo likely didn't even have it as an option. The Lincoln is definitely worth checking out though.

I won't try to guess %ages, but over the years of helping friends install stereos, I've seen LOTS of stock amps. My Eclipse had it under the opassenger seat, my Ford Probe had one near the rear wheel well. I've seen them in the trunk and in the dash as well.

I guess my point is to agree that it's more likely on a "premium" system, but never rule it out on any car (aside from say a Yugo). If you're already buying from Crutchfield, ask them what they have in their database on it.

One thing to watch out for is that the factory amps aren't always compatable with aftermarket plans. At a minimum you'll need a special adapter, at worst you'll find that it has certain built-in equalizing or other "features" that you can't stand, and can't bypass.