Riveria Inc, based in Cedar Rapids, Iowa, offered the hardtop convertible between 1963-1964 for the full / standard-size GM convertibles.
Such was GM’s production-line standardization, the entire range of models, spread over five divisions and three years could be covered by just three variations of hard top. Made from fiberglass with an external texture which emulated leather, weight was a reasonable 80 lb but the sheer size rendered them unmanageable for many and not everyone had storage for such a bulky item. The gradually growing size of the American automobile meant garages that easily fit a car only a few years early were now cramped.
Riveria offered their basic hardtop in black or white, a more elaborately textured model in gold or silver while the top of the range used the same finishes but with simulated “landau” irons.
No modification was required to the car, the roof attached to the standard convertible clamps, the soft top remaining retracted. Prices started at US$295 and the company seems to have attempted to interest GM dealers in offering the hard tops as a dealer-fitter accessory but corporate interest must have been as muted as buyer response, Riveria ceased operations in 1964.
thanks John, CoSC, and Steve!