I don't have the time/ costs for CX radiator replacement, but I remember someone telling me several years ago that a radiator change on a Plus Six was more involved and costly that a Plus Four, due to limited accessibility to the radiator. On the Plus Six the front wings have to come off, whereas I don't think they do with the Four??.

Dave
Plus Six "Squeak"
Roadster departed.
1936 BSA Empire Star Q8. 1935 BSA W7-35. 1938 BSA M20