RUN-Chilean citizenship (Santiago de Chile)

Hello,
I'm Lebanese and I'm wheeling to apply for Chilean citizenship but I need a little help...
My grandfather is originally Lebanese and used to live in Lebanon, where he got married and had 3 kids. He gained the Chilean citizenship when he went to Chile in almost Protected content he got married again and had kids too, then died between Protected content 1965.
Referring to the ministry of foreign affairs, I'm eligible to the Chilean citizenship, and I'm able to hold any sort of official certificates online only if I had my grandfather's RUN number, but he might not have had one if he died before Protected content year RUN number system was initiated …
I hope somebody helps me to find my grandfather's RUN if he had one, and if not, what should I do to prove that he was a Chilean citizen before he died?

I appreciate any sort of assistance.

Gaelle.