This tool is designed to cut a Ford FITS slot into any solid model. This has been tested in Fusion 360 and the steps for Fusion 360 are included in the Word document. Other modelling software probably has a similar function.

This is slightly bigger than a FITS adapter because it is designed to be used as a tool in the modeling process. The FITS adapter can be found here: https://www.thingiverse.com/thing:5913762