In many cases, the shaft spacing can be the same, but it is the subtle differences in the bezel area that make the difference.
For example, many of the pre-'67 C-body instrument panels might look like they could easily support a different or aftermarket in-dash unit, but when the flat aftermarket faceplate is put against the panel, THEN you notice lots of the subtle things I mention. We all want a factory-look radio to result with the aftermarket unit, but it might end up looking "hacked-in" many times. Some might do a better job than others in the addition, but still not completely "factory".
In the case of the '67-'68 Chrysler "thumbwheel" instrument panels, that subtle peak in the middle can be an issue. Better to use a flat piece to make that transition, which can also related to some diferent support structures behind it. Radios need a "back brace", by observation, for both radio chassis stability AND as a chassis ground path, for good measure. Even with a manufacturer flat panel, a radio with physical pushbuttons, due to the vertical angle, would still show the bottom of their pushbuttons "to the public".
On the 1969-'73 Chrysler panels, such negative tilt resulted in a few subtle differences. One is the pushbuttons were installed upside down, leaving what would normally be the shiny top surface to still be in plain sight when installed upside down. The other subtle difference is that the "dial" area is slanted rearward at its top to maintain a vertical orientation. Otherwise, an C-body radio would fit a C-body instrument panel.
For the 1974 model year, Chrysler standardized their B- and C-body radios into the flat panel orientation, which worked with a dedicated radio area of the panel. This opened the door for many aftermarket companies to offer "factory look-alike" products for dealers to sell to customers.
Then, with increasing technology and such, Gary Tayman and Aurora Designs entered the picture. Many companies were doing "retro look" radios with modern guts, but AD took an existing radio chassis and put modern guts in it. With better and higher-power audio amps, plus Bluetooth, USB, etc. in the mix. After first hearing of these conversions, it now seems that Aurora Designs has a USA-wide network of locations which can do these conversions.
Enjoy!
CBODY67