Fine Ian Rogers,
for some reason the OP did get only 1 digit.
i suggested him to add pull up on 74LS247 "rbo' pin.
the truth table shows like that and He need not leave them open, i suppose.
Can you perform Lamp Test(LT) checking how to do from the datasheet for the respective digits that refused to glow?
possibilities are that displays either faulty or model changed , unless the number tallies. you could sawap the LS247 chips one by one to the working display to check their performance.
Later restore to original locations and try swapping the display devices.
I assuem that you are working on Breadboard.