The most common engine in Zambia is the 1HZ and we use them for bush work and get a hard 450,000 km out of them before overhaul. The manual gearboxes never seem to fail but we swap out the oils annually and overhaul the front hubs. If you are mechanically minded then the car should last a lifetime.
Big job to sort out that rust and would involve taking the body off welding and plating etc so unless you are looking for a project car I would move on
Hub to fender distance remains the same but can be adjusted with your torsion bars. Yes hub-to-ground distance will increase with bigger (higher) tires
Cylinder head gasket coatings can deteriorate and allow a coolant creep into your engine and if your head is not warped then it is a quick gasket change. Lots of info on youtube. What mileage?
Just a couple of suggestions that fixed my vibration issues - try checking gearbox mounting or look for a distorted tire rim - have the wheels been balanced? The drive shaft (we call them propeller shaft) can also be checked for balance in addition a worn pinion bearing in the rear diff can...
Could always take the input pipe to the fuel filer and insert it into an empty bottle and turn it over for a couple of seconds to see if it is pumping?