Humvee-conversion and recoilless rifle

My next project is to make more recon-vehicles and
now the turn have come to my two Humvees.
I have adjusted the wheels and also sloped the back
of the cars to get the more characteristic look.
On the roof I have drilled a hole to be able to place
a heavy MG-gunner. The gunners seat is not completed
yet and I will glue more rivets and also fixate the
armoured-plates. 
I have used a simple plastic soldier that has its
origin in the matchbox range 1:32/1:72(US army WW2). 
This plastic figure is 1:48-scaled but the detailes are
very rough and therefore I have swapped the head and
used a more detailed one from Bolt action-US WW2.
I will paint Woodland-camo on these vehicles and I am
not sure if I will also put some camo-net on top.
I think I will try to make separate gunners seat with
figures holding a RPG for easy exchange.
A new report will be published when all this is painted
and finished.

Recoilless rifle: I am not sure what this is!? I have 
looked in books and also searched the internet and 
not been lucky finding anything. Probably it is a 
US M40 106mm but it has also features of a M-20 75mm.
Is there anyone outthere that have a clue?