Did you actually destroy an engine using modern grade oil?
Newer grades are supposedly bad (debatable) for old era engines but no hard evidence i think. Mostly just theories and stuff.
Well engine gets hot because combustion is going on in there.
It will be hot with LM as well as with any other oil. I don't think it should get extra hot with LM.
It should be little cooler with LM in fact as it is thickish oil.
SGO will do fine in winter but once weather gets hot, you'll feel the need to go little thicker like 20W-40.
CG is whole other thing. It will go fine with any oil. No nakhra.