M7 Motor Howitzer?

[kcw]

A relative today gave me a WWII photo of my dad, with carbine in hand, standing in front of what a first glance appears to an "M7 Motor Howitzer Carriage", sometimes known a a Priest when in the British service. My copy of "Janes" shows theM7 to have a mid mounted 105mm, the distinctive "cupola" on the right front corner supposedly having a .50 cal in it.
The unit in my photo however has NO 105mm gun (no gun there at all)...and the cupola barrel is much taller and appears to have a bit larger diameter than the unit shown in Janes, PLUS it has a gun which appears to be something on the order of a 75mm sticking out of it.
Anyone have an idea as to just what the unit in the photo might be?

[kcw]

Well, I figured it out. It's one of the M31 TRV series, this one with a dummy gun. Putting a glass on photo I can make out the vehicle ID number and see that it's assigned to my father's FAB. The buildings in the far background appear to be 2 or 3 story barracks, so the location is likely Fort Bragg. I assume that the M31 TRV (there are several in the pic) was being used for prime mover purposes for the units 240's during their training @ Bragg. When they shipped out to Europe they had M35 prime movers.

[emmagee1917]

All the M31s I've seen look like M3 Lees . Many , if not most , with a 3 inch pipe welded to the access hatch located where the main gun was on the M3 to make it look like an M3 . Some M7s had thier cannon removed to become infantry carriers , so it may be one of them. Also , I believe I read somewhere that the first run of M7s had 75mm guns , but was upgraded to 105s afterward. Can't find anything on that now , but I seem to recall that. Can anyone here confirm or deny this ?
Thanks , Chris