Evidence of Margaret Thatcher's support for General Augusto Pinochet prior to 1980?
I select 1980 as that was the date that Margaret Thatcher made a commercial decision in favour of British industry - not in favour of Chile or its Government. That decision was to reap benefits for Great Britain only two years later when British territory was invaded and occupied.
Allende's Government ignored the Chilean Constitution, one of the reasons it was overthrown. Pinochet was instrumental in ensuring that a new Constitution was drawn up in consultation with the people of Chile through referenda. He limited the term of office of the President and stood down when he had completed his own term of office.