not the most successful re-purposed a/c, but worth mention.....the CAC CA12 Boomerang. As a fighter it didnt shoot down even one enemy aircraft, ive read, and was supposed to have abeen a rapidly produced stopgap in the early days of the Pacific War. Despite vaiant efforts of CAC, it was not until August 1942 that the first CA-12s were entering service.
Despite this, the little aircraft had a successful careeer. It was used for target marking and used its heavy gun armamanet to good effect in CAS roles. It continued in its Fighter role, but was never challenged by Japanese air power in the operations that it was engaged in. It was not for lack of hazard that it failed in its role, just that opportunity to shoot down enemy aircraft never presented themselves during its career.