1988 318 engine

Your wife is a smart girl
The first thing I would do is check the chain, and the second is to do a compression test. If it passes the compression test, I would go thru the cooling system, and the fuel system. Only then would I start spending money.
If it oil burns oil, I would consider replacing the valve seals.

And I would check the EGR passage under the carb. They tend to coke up and eventually the choke won't work, and the carb will cook.
If it has a heat control valve in the exhaust manifold and it still works, service it.
Make sure the A/C belts are new, the system is topped up and it blows cold! hell knows no fury like an overheated I-told-you-so wife.

Check your tires.

If you're trip includes climbing up mountains, you better make sure you have plenty of cylinder pressure, that your trans has an oil-cooler, and fresh oil, and service your diff.
If your engine bogs down, when going uphill, and your brakes won't hold, you better be all prayed-up and ready to meet Jesus.