If you decide to change displays then one 'trick' that used to be used was to use devices with right hand decimal points to create colons. The display for the tens of minutes was installed upside down so it's decimal point was in the upper left, roughly above the decimal point for the ones of hours display. By turning both decimal points on you got a colon. Of course you would have to redefine the segment letters but I believe that many of the displays were symmetrical in that respect. You could also do this with left hand decimal point devices by turning the other display upside down.
Don