Contact Holden8702 on FaceBook for the 1/72 scale US Vietnam War arty crew figures. Ask him specifically about getting copies of the Project FSB RIPCORD figures.
Here are some “happy snaps” of some of the figures that he made for us in a few of the various vignettes on the diorama.
I don’t know the details about their removal or installation, but the devices you have circled are brush guards / deflectors for antenna bases.
Someone who knows the technical history of the M113 might be able to offer up a timeline as to when those were added (if they weren’t original to the design). Could be - and I’m just speculating - that the guards / deflectors were not original to the design so they were added later as field mods or during production.
We had what seemed like a gazillion figures to paint, so only some of the “hero figures” got more than superficial finishes. The sculpting and 3D print quality was quite a lot better than many of the pictures might otherwise suggest. Holden did really good work for us. A number of the figures he made for us were based on contemporary photos taken on FSB RIPCORD.
FSB RIPCORD commander LTC Lucas (later KIA and awarded a posthumous MoH) and PAO photographer Christopher Jensen at the entrance to the command bunker. The signage was well photographed and the map board was used to brief visitors on the situation, The black sign over the entrance dates to the initial occupation period when RIPCORD was occupied by both 1st ARVN INF DIV artillery and US 101st ABN DIV arty and infantry. Even after the ARVN arty unit was redeployed to a different firebase, the original sign remained.
Those are guards for the antenna bases to keep them from getting broken. They were only mounted where the antennas were mounted and in the picture, you can actually see it sticking up beside the antenna base.