Is a 2008 Chevy Monte Carlo basically 2 door impala?

Not exactly. While both the 2008 Chevy Monte Carlo and the Impala shared some GM platform components and were both rear-wheel-drive (RWD) sedans for a time in their history (though the later Impalas were FWD), they were distinct models with different designs and target markets. The key difference is the Monte Carlo was a two-door coupe, while the Impala was (and is) a four-door sedan. That's a fundamental difference in body style. They didn't share the same body at all, despite some shared underlying architecture.