Andre Pradeau, from Limoges in France, built a series of small capacity cars during the 1950s and early '60s, one of which used a JAP 500 engine. Sadly we do not have many details of this car. But it did show up (unrestored) at the Goodwood Revival in 2016. Photos courtesy of Rob Young.
This photo is of a later car, a prototype for the Formula IV which was killed off by the introduction of Formule Bleu which used Renault engines.
If anyone has any more details, please get in touch.