The M15 is the half-track version. I believe the truck is the GMC CCKW-353 2.5 ton 6x6...the deuce and a half...
That's from this page on Tanxheaven...
http://tanxheaven.com/ludob/GMC-CCKW-353lb/gmccckw353lb.htm
More specifically, it does look like there's a French connection. Check out this pic...
That looks like it to me. It and a bunch of other great pics are on this page, along with lots of information...in French....
http://perso.wanadoo.fr/jp2k/2db/materiels_gmc_bofors.html
Using an automated translator, this is what it has to say about the vehicle...
The 22e Colonial Group of Force Terrestrial Air (the DCA of 2e dB) being gradually equipped in the trucks GMC, it is on November 24 1943 which the first GMC (6x6 of 2,5 tons CCKW registered 415920) is equipped with one piece of artillery of 40 mm Bofors (Mk1 or Mk2). It is with the field of fire of Aïn Diab then on the field of fire of Mediouna that the first shootings were carried out. Following several expertises and controls, it is decided on January 12, 1944 of the transformation of 16 Bofors of the groupen, out of self-propelled guns.
According to the tactical letter, this GMC Bofors would be the reproduction of the GMC Lucifer of the Sergeant Wonder. It acts of the 3e part of the 1ere section of shooting (the latter gave names of the hell to its vehicles.) belonging to the 2e battery of shooting.
This reproduction is not free from errors. The registration of Lucifer was 417404 and not 417386 like sight on the photographs. As well as the American flag on the corner of share-breaks... The site of the letters tactiques..etc.
Lucifer sounds like a good name for it.
Oh here's one more pic from the French site...
And a great looking build I found on a Russian page...
That one and more pics here...
http://vif2ne.ru/smf/forum/2/gallery/Megas/000009C005213A4D/get
Oh, and there was one more interesting one I saw...one with armor used in the French Indochina War...
http://indochine.net.co.nr/cefeo/afvs.html
Looks like an interesting kit.
Karl