Resicast makes a couple of conversion kits in resin ( 1/35 ) that might give you an idea on how to add kit to your jeeps 
The gun jeeps look rather simple , aside from adding stowage every where , they changed/ removed the passenger seat up front with seat from the rear . The flame thrower version ( Warlord resin kit parts maybe ? ) was a one off . The pictures of actaual vehicles I have found are rather grainy , being 60 plus years old who’ld of thought , but the re- enactor type vehicles seem to look the part . Popski’s book might be something to get as well , seems to be going cheap on various book sites . There was also a few comics that covered PPA , might be good for a giggle
