20 years with a 78 , been there and back.
From HZ1 to HZ +turbo, to finally HDT .
il you want a more road truck , go for 24 val .
THE problem today is finding a good HDT !
Swap is vero easy AND quick .
Just my 2 cents
Wow ! What great mountains 😳
What is that in the last photo ? K2 ?
If you are driving at high altitude , the overheating is probably due to excess fuel , or too little oxygen.
Toyota has a high altitude compensator , HAC .
But you must accepte that the car has less performance at high altitude!
Looking back at your story , I see that you have a HZ1 + turbo , not a HDT engine .
There is a huge diffrence in this !
Hz1 + turbo are running close to their limit !
And only a good IP even better with a Dyno track can set it right .
Certainly not a big radiator.
Try to make 1/8 of turn on the...
It you have overheating on a HDT engine , you must find the source of it .
That engine doesn’t overheat , never ever !
No need to install a bigger radiator.
Pls check the thermostat, might be locked or you have bubbles in the cooling system .
Assuming the engine is sound ☝️
I have a disconeted solenoid Wienerwald I park my 78 .
AND a secret but pratical Swatch, for on/off .
Catch the wireless behind THE fuse box .
Will avoid General thiefes , but not pro.
From the look of THE oil in your differential clearly you have a water contamination.
THE chunks of metal that you found are a sign of heavy or improper use .
Best world be to have a deeper look in to it .
From what I See in THE Photo , everything is rusty . A easy fix is to weld a 5 mm hard steel plate ,as base for THE spring. But expect other failures as rust never sleeps !