In the golden age of racing aircraft there were attemps to transform racer designs into interceptors with minor modifications. I remember the Huges H-1 which was entered into the USAAC 1935 Fighter competition (won by the Seversky P-35). If my memory is right no single raced was ever turned into an efective interceptor. Another question is racer technology transfered into fighter designs.
The racer is designed only for speed. A fighter needs speed but that has to be matched with a many other qualities that need a quite different design. Some racers are similar to some fighters in their external shape but nothing more.
My conclusion is you can go racing into a little mod fighter but don't try to go combat into a racer.
Italians tried to convert the Breda Ba 88 sport aircraft in a sort of light bomber and it turned out to be a real mess.
Despite the protoytpe's performances the operationa aircrafts were a complete disaster....
The webpage i cited says that it was a c.3 enterant wich was kind of a 3 seat fighter and awacs combined. the idea was that a comander in the 3 seater would direct single seat air craft in combat in reality this proved un workable as the comander would be unable to keep track of the battle while manauvering.
The Caudron C 670 was corresponding to the conditions of
the 'Programme Technique des avions multiplace léger de défense'
techical program light multi seat defensive aircraft.
better know as-l'avion de représailles-(repraisel aircraft-COIN)
A version as recce aircraft was planned.
No mention of the c3 program.
source :Fanatique de L'Aviation-March 1973-pages 26-29.
On Page 560 of Flight for7 June 1934, shortly before the MacRobertson air race, it was reported that:
“The MacRobertson Interceptor” According to an American contemporary, the British Government will seriously consider the adoption of the winning machine in the England-Australia race for modification as an interceptor fighter.
The winning Comet was duly purchased by the Air Ministry, serialled K5085 and evaluated by the RAF. De Havilland tried to sell the idea of a fast, uncatchable reconnaissance bomber but at the time the Ministry declined. Nevertheless, the Comet is almost exactly the same size as the Spitfire and Hurricane prototypes then under construction and the Merlin fits it like a hand in a glove, so I decided to see what a Macrobertson Interceptor would look like - see below.
Needless to say, when DH had another stab at the speed recce/bomber, they stuck two Merlins in a much bigger Comet and the rest is history.
Yet, extraordinarily, back in 1935 de Havilland had already been asked to study a high-speed bomber variant with a 1,000 lb payload for a secret bombing mission. G-ACSS/K5085 was meanwhile rescued from the scrap heap by FE Tasker, who re-engined it and engaged his old partner A.C. Clouston to fly it on various record attempts. Then in 1938 a Jewish millionaire contacted Clouston with a plot to assassinate Hitler - I kid you not. The thoroughly-researched plan was to bomb his car during a ceremonial parade. Clouston was offered a million pounds but, not fully appreciating the plight of German Jews at the time, he declined. The tale is told in his autobiography, The Dangerous Skies. A link between the secret design study of 1935 and the offer to Clouston is an obvious guess, but I know of no direct supporting evidence.
The French also contemplated clandestine reconnaissance flights over Germany using their two existing Comets F-ANPY (formerly G-ACSR) and F-ANPZ but none ever took place.(ref. Philippe Ricco; "La Comète en France - Part 2 - The burden of proof". Aeroplane Monthly, Vol. 38 No. 449, September 2010.)