Welcome Bush Buck!
Glad to have you aboard, and we will love to hear of your adventures! Make sure you post a lots of pictures of your adventure.
A few questions that come to mind when planning an adventure such as this. Are all of the vehicles taking part in the rally going to be of the same type of vehicles? This would help to pack a few of the vital ignition parts that would interchange within rigs. Are there any trailers being brought to hold extra parts/supplies/camping gear? Depending on how much room you will have to store parts, I would pack enough spares as you can stand to carry. The assumption is that you'll need to carry extra fuel and water for the trip, you'll be limited to the extra room to bring too much of the larger items.
Below is a Jeep adventure using bone stock Jeeps going through South America in the late '70s. Great read, and some information that may help you in your planning. It was a different environment, but still can help out.
https://www.hemmings.com/blog/2014/0...-las-americas/