Question regarding United inaugural revenue 727 flight(s)

Can anyone provide me with the date and flight number of United’s inaugural 727 flight from DEN to SFO in early 1964. I was on that flight and still have the commemorative plate that was handed out to each passenger.

I seem to recall that United might have actually had a pair of “inaugural” flights that day; one eastbound from SFO to DEN and the westbound flight I was on. I don’t know if it was simply one aircraft that flew a round trip or whether two different 727s were used simultaneously.

Any insight would be appreciated.