You can choose two 4-bit digital pipes so that only two I/O ports are used. ***Yang's digital tubes only need one triode driver each, 9014 or 9015 (which are pnp tubes, wired the opposite of 9014)
Also for you (51 series microcontrollers have 4 I/O ports, each port is an 8-bit quasi-bi-directional port, *** taking up 32 pins. Each port includes a latch (i.e., dedicated registers P0 to P3), an output driver, and input buffer. (The four ports are usually denoted generically as P0 to P3.)