Wildcat
Major
I didn't think the R2800 was relevent as they didn't have any engines.
But it does prove that the CA-15 was not based or was not a modified -51, but an completely new design.
The CA15 was based on a Mustang (hence a similarity)
Wrong, It's a common misconception that it was based on a Mustang because of its similar looks. The CA-15 had a longer and bulkier fuselage and its operating weights were also greater. The need to install the inline Griffon instead of the R2800 necessitated the use of an under fuselage radiator which, coupled with the streamlined look of the Griffon, gave the CA-15 its "mustang" look.