Hello Chevy man,
My first question is why you are using a 16C54, which is a one time programable PIC. There are a lot of newer flash devices, which often cost less than the old OTPs.
That said, you want to use a parallel in, serial out shift register, like the 74hc165, or 74hc597. Basically, you first latch the data on the shift register (if it has a latch,) then you shift the data in the register into your pic with the serial clock pin. Each These can be cascaded, which adds an extra pin to the circuit for each chip. It will take only three pins of your pic for the first shift reg, and one extra pin for each additional register, so for 16 bit input, four pins of your pic. The data sheet for the shift register you choose will give you the timing requirements for the chip.
By reading the data sheet, you will get the idea of which pic pins to toggle, at which times, to shift the data from your shift reg into your pic.
Hope this is what you were looking for, but feel free to ask more questions.
Best wishes,
Robert