They don’t necessarily need 67 - only “two-thirds of those present”.
I think that only means 2/3 of whatever number constitutes a quorum.
In the Senate, a quorum is a majority of the body, so 51 members may do the business of the Senate.
So, 35 members is 2/3 majority in the Senate with a minimum quorum.
It should be noted that onerous gun legislation has passed the senate with only 3 senators present. Bob Dole could have stopped it by suggesting a quorum was not present, but he supported the bill, so he remained silent. Passed unanimous on a voice vote.