If Z17 is getting too hot to touch especially compared to Z16 which is the same chip, then your instincts are probably right and it's fried.
This might sound odd, but take a sniff of the area around Z17 with it on. You might notice it giving off a certain smell. Next time you're working on a logic board and notice that smell you'll know somethings cooking.

The heat check is a very good indicator that Z17 is faulty especially if it gets hot within a minute and it's twin neighbor at Z16 stays cool and produces valid digits.

You can put one of the working displays onto the output of that Z17 chip - i.e. move the display at player 1 to the player 3 position and see if you now get legible digits.
Download the datasheet for the 7448 chip at Z17 which is a 'BCD to 7 segment decoder'. The logic datasheets usually have a truth table indicating how the outputs react based on the state of the inputs. That datasheet also lists all the output numeric display combinations which can help determine if it's producing valid outputs (presuming you have no connectivity issues from the MPU board to the display).

Any chance someone has socketed your Z16 and Z17 chips in the past so you can swap them around?

You have corrupt data in the battery backed RAM. Go and clear the book-keeping audits and reset the score level awards and highest score thresholds.

PinMAME does the same thing showing 70 in the Ball in Play display on powerup so presume it's normal. It also doesn't show any lamp attract mode sequence so it's also probably normal that no lamps are flashing.

At this point you should try and go into test mode and look for switch and solenoid/relay issues.