As we used to say, YAT YAS! Good looking Amtrac there Rex. I have two myself and am working on a third. The Marines used all the versions of the Amtracs as they became  available. They didn't discard any of the old versions though and units were still using LVT 2's during the battle of Okinawa late in the war. You are correct that LVTa1's were used at Iwo Jima as were the LVTa4's.