Larry:
Ya got me !!! I went back to check my pix & the best one of a Mack NO & Long Tom in fact didn't have a limber !! I thought the limber was just hidden by grass, but on closer inspection (length of the truck + gun), it isn't there. I'll post it later because it is a neat pic anyway. Further quick search yielded nothing, so obviously I wasn't paying close attention. I'm ashamed.
I went back to TM 9-350 (the M2 155) and it says something like "without limber by being semi-trailered" but as I said -- no pix, no other explanation.
I did find the "Catalog of Army Vehicles of WW2", a reprint of a 1944 manual where, under the 7-1/2 ton Truck (pg 112) it states "An Ordnance pintle, Model M-5, is furnished, together with special coupling attachments for the 8" Howitzer, M1, and the 155mm Gun, M1." Guess I need to look for a Mack NO TM.
Does the Mack NO model come with such a "special coupling" ??? If so, a picture of that or the instruction section would staisfy my curiosity. If not, then how will you hook 'em up ?
The only French book (like what you suggested) I've got is one on markings .... no joy.