Darren,
A two-way speaker is a woofer and a tweeter. A 3-way adds a mid range to it.
I don't imagine there are any 4" speakers out there that can handle much power, but by the sound of what your radio puts out, it should be do-able. You might want to check out Crutchfield dot com.
I know this is an A-Body, but E-Bodies had a depth limitation with dash speakers unless you wanted to hack away at the dash frame. So be aware of the dimensions too.