I'm going to also throw in my $.02...

I spend from the mid 1970's thru the early 80's exploring/ surfing/ bumming around Central America. Over that time I drove from to and from Panama twice (from SoCal). The first time I had my Land Rover so crammed with spares that my girli and i could barely sleep in the back... And it still didn't help me when I "grenaded" my rear 3rd member.

Then 2nd drive down I took a Jeep and next to no spare parts because I learned that there are really good auto parts stores in just about every town of any size and dealerships of virtually every brand of vehicle in the capitols and major cities. So in the worst case scenario, You will have to leave you care in the trust of a mechanic and take the bus to the capitol to get parts, but more than likely you will be able to call them and have the parts put on the bus to your location!

It was not much of an issue 35 years ago! So, don't make it one now.

Make sure that you have VERY GOOD fuel filtration!!! Carry more than one extra primary filtration filter. Drain your h2o trap often! Also have a liter or 2 of fuel additive with you at all times. Bad fuel is going to be your #1 problem. One way to make sure this issue is minimized is to only fuel up where the semi's are filling up. Make sure that you have a full Jerry can with you at all times. Trust me you will end up in areas that are "waiting for the fuel truck to arrive.

You do know how to prime your fuel system, right?

The next big issue on making sure that you keep your drive line lubed (I'm not sure whether there are u-joints on your year wagon). If there are make sure you have spares.

make sure that you have a little strip of emery clothe to sand electrical connections. Corrosion is more than 90% of all electrical problems. Vaseline is good for coasting connections

It is also a good idea to mount you rear licence plate with a buttonhead Allen bolts so that it can't be stolen. Take of your front one and stash it in your car so that it the rear is taken... You have a spare.

Have you made "blackout" curtains for the wagon so that you can sleep on city streets without getting rousted? For that matter, keep all your possessions out of view with curtains or simply a tarp. Most theft in Latin America is "crime of convenience".

Do you have a hidden lock box securely mounted in the wagon for your valuables? If not, I'd delay your trip and get one welded up before you go!

Have fun and only eat in crowded & popular restaurants.