Driving 7-Segment Displays using a microcontroller
Regardless of which way you choose to go, you're going to have to share some of those 70 "used-up" I/Os with whatever you're going to use to drive the displays, so I suggest you use four of them, [I/Os] go the simple hardware route, and use a couple of TI 16 channel LED drivers for just long enough to update your displays periodically.