If it was a season 5 episode, it was most likely N7264U, a 727-200:1
Registration N7264U, c/n 21411/1346 built in 1978 for United. Based at Ontario International Airport (ONT/KONT) in California, where this was most likely filmed.
The 727's three Pratt & Whitney JT8D engines are all mounted on/in its tail, and the plane was large enough to have six-abreast (3+3) seating, as can be seen in this 727-200 seatmap found via a quick google (this particular seatmap is for an EAL 727, but the 3+3 seating was common to all passenger 727s of which I am aware):
(Image by Eastern Airlines, via Darren at Frequently Flying.)
And the 727-200's maximum passenger capacity was 189, according to Wikipedia, although it more usually carried 134 (in a two-class configuration) to 155 (all-economy arrangement), so it fits the 150-180-passenger requirement (and even exceeds it slightly at the upper end).
And yes, I know it's a trijet, but:
- the #2 engine is buried within the 727's tailcone and mostly concealed from view, unlike the large, obvious pods holding the #1 and #3 engines (as opposed to, say, a DC-10, whose centerline engine and associated intake duct form a huge conspicuous cylinder above the fuselage at the base of the vertical stabiliser);
- as for the centerline engine's tailpipe (which is visible, sticking out the tip of the tail, if you look carefully), the JT8D is a slim low-bypass turbofan, making for a much narrower and less obtrusive tailpipe compared to the chunky high-bypass engines that occupy the tailcone of (say) an L-1011 or Yak-42;
...and, putting both of those together, and considering that it was a (presumably brief) cameo giving no reason, and little opportunity, for you to pay close attention to the tip of the aircraft's tailcone, it's perfectly possible that what you saw was, in fact, a (trijet) 727, and that you simply didn't notice the easy-to-miss-at-a-brief-glance middle engine.
1: Thanx to Gerry for providing the link.