You mention the cowl tag/ data plate indicating the correct interior, but the code should also be specific for not only the color, but for bench or buckets (Okay, I am not a 65 expert). So by being able to decipher that code, you should be able to determine what the correct seats would be.
Console brackets would only be installed if the car was to get a console. Have you looked for inner bucket seat mounting brackets?
The same goes for the "shifter hole" in the floor. There was NO hole if the car had a column shifted transmission...
I personally doubt anyone would pay the dealer the money for the SS option and then have the dealer replace the buckets with a bench seat, when you could order a Malibu with the same drivetrain... I am sure it would cost far more money and time then to just find the correct options in a Malibu. If the dealer were to pull a "new" seat out of another Malibu, where would the buckets go (no brackets on the bench seat car). And how long would it take to order a new seat, as opposed to finding another car?
Remember, on the early SS cars (up until 1966), the SUperSport package was NOT a performance package, but a styling package (buckets, console, guages, trim). This was true for Novas, Impalas and Chevelles. They were available with 6 cylinders as well as most any V8.
From what I have read, the option to have a bench in an SS started in 1966.
Steve, you got it backwards here... In 1966, the Bench seat was STANDARD on the SS
Chevelle. Buckets were an option, as was the console, and the guages, etc. The 1966 SS only had the additional trim and the 396 engine and 12-bolt rearend. Pretty much all the fancy stuff was optional. The Base 1966 Chevelle would have a 325HP/396, 3-speed manual on the floor and a benchseat, 12-bolt non-positraction rearend, no guages or tach. Pretty basic. All manual transmissions were floor-shifted, but the Powerglide could come with the optional column-shifter.
This is the first SS car where the SS became a performance option with all SS cars having the 396 engine.
Anyway, back to Tropos car... Its possible that the seats/console/column were taken from the car at some time in the past 37+ years, and a subsequent owner replaced them with what he found. Two-tone fawn was a pretty common interior color. If the front seat looks old, its probably from a Malibu (I think the 300s all have cloth seats). Or maybe they used a repro seat cover (been around for years) or an upholstery shop copied the back seat.
why don't you post the info from the data plate, and someone can help decipher it...