Art…..as far as hard parts, body style for body style, just about everything fits. That is to say, dash panels, instruments, seats, switches, window moldings, etc. are all the same. Trim, however is quite different. Closed cars used a combination of vinyl and cloth for their seat upholstery. The cloth for Star Chiefs was an upgrade from the Catalina, and the Bonnevilles were upgraded from the Star Chief. Bonneville convertibles had genuine leather seating surfaces as standard. Leather was also an available option only on all Bonneville closed cars. Catalina convertibles and Safaris came only with all vinyl seating. Door panel trim had various designs embossed in the vinyl depending on the model. Therefor, even though a Bonneville Vista panel would fit a Star Chief or Catalina Vista, it would not be correct. One good example of this is a pink Catalina convertible, that Harley Earl had made for his wife. It had a complete Bonneville interior installed, and sold a couple years ago at Barret-Jackson. Catalinas also had a different design for the window crank handles than the others.
There are some trim differences for the instrument panel. Even though the panel itself is interchangeable, the Bonnevilles and Star Chiefs had the bright trim across the panel surrounding the cluster and radio. Catalinas did not have this. There was also a chrome strip going across the lower dash that spelled out "PONTIAC" on the ashtrays and glovebox door. This was standard on Bonnevilles and Star Chiefs, but optional on Catalinas. Bonnevilles and Star Chiefs came standard with a clock and two speed wipers, while these were optional on Catalinas. Padded dash was standard on Bonnevilles, optional on all others. No cars but the Bonneville had the assist bar on the right side of the dash. There may be some other minor differences that I left out, but these are the main items……John