10, ,,,,,CGI was'n't used back then.
Actually it took a few hours of sitting in a make-up chair to get an ape-sized guy looking like an ape-sized-ape during that production ... if I am recalling this correctly.
Back when the original Planet of the Apes was filmed, the 'apes' had to go through a very long make up process (six to eight hours if I recall correctly).
I can recall getting a phone call while I was stationed on Okinawa encouraging me to take some leave and be a participant in this first Ape production, but that leave was an impossibility.
Then many years later I get a call from a family member who said that he was sitting in the make-up studio to become an ape which involved a very long association.
I was not involved in that production but I did have the opportunity to watch the ape 'transformation".
Oh yea, and Orville Burke as also an ape in transformation two chairs over.
Small world right there.