In the original story, in the room at the Riverton Motel Siesta, in 1967, when the guys are on the bed, Jack does mention seeing a pair of binoculars hanging on the rearview mirror in Aguirre's parked vehicle when he goes back to reapply for a job upon Brokeback Mountain in 1964.
As far as the book goes, Jack knew absolutely nothing about the Aguirre binoculars in 1963. Jack did tell Ennis that Aguirre said when Jack went back, see the following from the book, "Got to tell you, friend, maybe somebody seen us that summer. I was back there the next June, thinkin about goin back -- I didn't, lit out for Texas instead -- and Joe Aguirre's in the office and he says to me, he says, 'You boys found a way to make the time pass up there, didn't you,' and I give him a look but when I went out I seen he had a big-ass pair a binoculars hangin off his rearview."
But, Jack neglected to mention what Aguirre said about letting the sheep babysit the sheep while they "stemmed the rose" and that Aguirre had declined to rehire him.
Kd5000, I also see contradictions in the film version of the story, the screenplay version(s) of the story and Annie Proulx's original short story.