Let’s take a look at four renderings done as part of the development of the 1973 Colonnade cars; the Cutlass in this case. This fastback has a number of elements seen on GM cars, including the Monte Carlo-ish fender sculpting. It even has the cabin ventilation exhaust openings as were used on 1971 cars, but on the sides. The tail looks like it made the cut to the final car.
The colonnade roof is on full display here, as are the reverse scallops on the fenders. Yet it manages to not quite feel that much like the real thing. Maybe because it comes across so trim compared to the production car.
This doesn’t seem to have contributed too much, except the rear roof line.
Even more so the case here. Feels more Pontiac-ish.
Here’s the real thing, in case your memory banks need refreshing. And here’s the CC for it, if you can stomach it.