You're welcome.
The board did go across the opening of the hatch. In this link, it shows how I placed it on a model of a track that did not have the full ACAV set of shields. The crew of this particular track (I model actual vehicles people I know or am in contact with), just used the board for a seat.
https://www.modelersalliance.org/forum/james-o-leary/153737-afv-club-m113-acav?start=120
If you look through the rest of the thread, you will see the project from start to finish and it may give you some ideas about how to go about your interior. Here's a photo of the figure I added to the model that shows how the gunner would sit on the board:
My friend, Bill Rambow's crew used a board as well, but they covered it with a sandbag of softer sandy dirt to make it a bit more comfortable. The gunner or TC would sit on this, lean back on the hatch, and place their feet against the mount for the .50. In my diorama, "Breakfast in the Boonies" which depicts Bill's track and squad, you will see some of the details that make his track a bit unique. They had the 106mm Recoilless Rifle mounted on the right side, an ACAV shield on the left side for an M60, and then only had the tub part for the commander's cupola. The reason they did not have the big shield on the front like most ACAVs was that it interfered with the 106mm RR.
Here is the link to that thread:
https://www.modelersalliance.org/forum/just-like-the-real-thing/152358-breakfast-in-the-boonies-vietnam-july-1967
Most modelers tend to think that every track in Vietnam was equipped with a full set of ACAV shields. For the most part in Cavalry units, the majority of the tracks were equipped with full sets, but in Mechanized Infantry units you could see tracks with no shields, to partial sets, to full sets. It depended on the time period as in the beginning of the troop buildup the priority for ACAV shields went to Cavalry units first and then were distributed as available to other types of units.
My main advice is to figure out what unit and time period you want to depict. If there is a specific track you want to depict, try to obtain as many photos as possible of it from different angles. Perhaps read about some personal accounts or get in contact with a unit member, or better yet, a crew member of the track being depicted. This will help you figure out which version to build (M113 had smaller gas tank and white interior; M113A1 had the larger fuel tank with a very light green interior).
Keep in mind that not every track in Vietnam was equipped with ACAV shields. Most Mechanized Infantry units used whatever they were able to get their hands on, so in those types of units you may see all kinds of unique configurations (which I think make for more interesting models).
Good luck on your project and I hope to see your in-progress photos.
Cheers,
James
ldguy Gary XXXXV XX XX
