I've just been hunting around for possible alternative display donors and found this interesting site:
http://www.vintagecalculators.com/
The Texet 880 is one variation of what that site calls the 'standard type 2', a model which was sold branded with a number of different brand names. Some changed the brand name but kept the '880' model number, others went entirely their own way.
What I notice from that site is that many of the models described as '8-digit' actually have a 9-digit display with the leftmost digit not used. You can see this on many of the images where all of the displays which can be lit up are lit up, but there is an extra unlit cell on the left of the 8 lit ones.
As Hysteresis pointed out, an 8-digit display will work just as well in the MK14 if its pinout corresponds to that of digits 2-9 on the original 9-digit displays.