I think this was discussed in a previous post.
It looked like there was no brake booster in the photo I saw.
A land rover six is an odd conversion to do for joe public, but you make a good point about it possibly being in service. It might have been a training exercise maybe? Don't know how the army system would handle it!
From memory, and in theory, it should have bigger brakes and booster and the firewall should be different.
Did the production sixes have Rover or Salisbury diffs? If it's a rover one, I'd be a tad worried about axles!