Hi Pump 150,
I think I have found a photo of SGT Vanderwall, at least I think I have. It looks a lot like the guy in the pic you showed of SGT Vanderwall getting decorated. I'll post it below, but first some background.
I came across this site while doing a Google search on D 1/9 Cav operations in RVN. In Jan/Feb 1970, D Troop, 1/9 switched over from gun jeeps to the V100 Commando armored car, made by Cadillac Gage. The Army designation was M706, but they were usually called "Ducks" by the GI's, because they were amphibious.
A friend of mine currently has a 1969 V100 (beautifully restored) with D 1/9 markings. It's a big hit in parades and at veterans events. I began researching the use of the vehicles by D 1/9 to see how they were painted/marked and how they were armed/equipped in theater. I eventually ended up compiling about 10 photos of the D 1/9 V100 vehicles (and the men of D Troop) from the 1970 time frame.
Most V100 pics from Vietnam (easy Google search) show them in their common usage as truck convoy escort vehicles, first by the ARVN in 1967 or so, then with widespread usage by US Military Police units from 1968 onward. The MP's too started out using gun jeeps (like D 1/9 Cav), but were eager to get the armor protection of the V100.
Vehicles from D Troop 1/9 Cav are instantly recognizable from the yellow "diamond" marking on the vehicle sides (D as in Delta, D as in Diamond) . Alpha troop choppers had triangles, Bravo 1/9 choppers had squares (box), Charlie 1/9 had circles and Delta 1/9 had diamonds. So, if you see a yellow diamond, it's 100% a D 1/9 vehicle. And if you see a V100 with a yellow diamond marking, it is definitely D 1/9 from Jan 1970 or later.
So with that said, I found a pic of a V100 with a yellow diamond on it and the guy standing on the front of it is (I believe) SGT Vanderwall. It would be a D 1/9 Cav vehicle and it would have to be on or after January 1970. Based on your post about the grouping you have and the SGT Vanderwall's service record you included (he was an armor crewman in D 1/9 from Jan 1970 onward).
The actual pic is a big file and is remarkably high quality for an amateur photo. I had to drastically crop it down to just showing the man in question to get under the posting size limit for this forum. Please compare it to the pic in your post that shows the decoration ceremony and let me know your thoughts. I'll email you the full sized pic if you think it's the same guy as SGT Vanderwall. It'd be a great addition to your grouping if it's him.