Thanks folks. The following are likely the last of my belaboured Dewoitine musings ...
After proving the prone-pilot concept, the AE-PCV testbed (see post #701) was rebuilt as the M.520TP (Turbo-Propulseur) to flight test the new SNECMA-Rateau TB.1000 turboprop engine. The goal was to demonstrate the main powerplant installation for a proposed SNCAM 'Propulsion Mixte' attack aircraft to Aéronavale's 1947 specification. This M.900PM (intended for new PA28 carriers) would have a nose-nosed TB.1000 producing 1450 shp for take-off plus 570 lbs of thrust. This was boosted by a tail-mounted Atar R.102 Hestia turbojet producing another 2,500 lbs of thrust.
The M.900PM's turboprop installation was a complete success but the TB.1000 engine proved capable of only 1240 shp (+550 lb.st) and as little as 940 shp (+ 190 lb.st) at cruising speed. While there was hope for performance improvements from the TB.1000 turboprop, SNECMA elected to concentrate on its larger Atar R.101 turbojet and to stop further development of the R.102 Hestia. That brought the planned M.900PM to a halt, Aéronavale choosing rival designs from Breguet and Nord-Aviation instead.
In the meantime. SNCAM had developed a straightforward turbojet derivative of the D.520 incorporating the AE-PCV prone-pilot position. The M.780 was intended as a simple, rough-field attack aircraft. D.520 wings were retained as was the tail arrangement from the M.521V. Power was to be provided by a single Atar R.100 an improved SNECMA variant of the wartime BMW 003 turbojet. The M.780 did not especially interest the AdlA -- the armament choice of four smaller Matra MG 151 20mm cannons being one cause for concern. But it was a moot point since SNECMA would soon cancel its R.100 to focus on Atar R.101 development.
For those keeping record, the SNECMA-Rateau TB.1000 turboprop was real (although it was eclipsed by the AS Mamba) as was the contest for a new attack aircraft for PA28 carriers. The latter led to the Breguet Br.960 Vultur prototypes (which, although unsuccessful, inspired the ASW Alizé). Other than the Atar 101, the turbojets are pure whif -- SNECMA's work sprang from the BMW 003 but, AFAIK, they had no intention of actually producing the German type. The 'R.102 Hestia' was, of course, inspired by the later RW Atar R.105 Vesta, a reduced-scale Atar 101.