I remember working at Airline Engineering, (Monarch) back end of 1979. They aquired another B720B from Maersk.
We were fitting the seats and PSUs for 179 seats but when we got to the back of the LH side the seat rails stopped about 2 ft short of normal so we were told to just move all the seats forward to make them all fit.
I think the seat pitch was about 28 ins for quite a few rows. This aircraft was going on charter for P&O cruises to the Far East. I'm glad I wasn't a passenger being 6ft 2in.