Chrysler civilian production engines were always painted a light grey with fittings like generator, starter motor etc black.
I believe this to be true of these trucks as well.
The 'gantry' you mention is the bren AA mount
__________________
Cheers
Cliff Hutchings
aka MrRoo S.I.R.
"and on the 8th day he made trucks so that man, made on the 7th day, had shelter when woman threw him out for the night"
MrRoo says "TRUCKS ROOLE"