Erik is correct, it is always better to use a chip with higher Program Memory(atleast enough for ones requirement).

However if it is must for Mr. Frank to use external code memory,

Then one simple way (of the many) is to use address/data bus (sacrifycing P0 & P2)( I hope he is not using 2051 or similar) connected to address & data pins of memory through a latch(74hc373). Generate necessary Enable signals(use /RD pin of mcu). use some decoder(3:8 e.g. 74hc138 or 4:16 e.g. 74hc154) if needed

Ofcourse, this approch leaves you with more than 17 port pins short(few pins needed for decoding logic). If remaining pins are not sufficient can add ic like 74hc244/245/373 for port expansion. Or can use 8255 (this will give you 3 additional ports). [remaining o/p of hc138 can be used as chip select for 244/8255.]

At my first job my first project was requiring 8 ports(15 i/p lines i.e. 2 ports approx & 44 o/p lines 5.5 ports). also UART & both interrupts were necessary & few more electronics.
Here I had used 3 no of 8255 selecteed through a 74hc138)

This was only for general information

Regards,
Mahesh