Question: Was it intentional that Joe Namath and Ann Margaret's names were each repeated twice on the screen as Sharon Tate walked into the theatre? (01:08:00)
Question: What does Tex mean by "I'm as real a donut motherf'r?"Something significant?
Answer: To put some context into the scene, three members of the Manson family (Tex included) have broken into Rick Dalton's house and are holding Cliff Booth at gunpoint. Cliff, who is high on drugs asks "Are you real", to which Tex replies "I'm as real as a donut, mother fucker." Tex was trying to answer Cliff's question stating whether or not he was real, but in the most intimidating way possible, and I guess donut was the word that came to mind that described how real he was.
Answer: Yes, though the intention was not Tarantino's. What is onscreen is the trailer of the (real) 1970 film "C.C. and Company", which starred (as you might have guessed) Joe Namath and Ann-Margret. Said trailer showed their names twice, a stylistic choice that emphasized the film's stars, and Tarantino used the unaltered trailer in the film.