Yes Mike, I have seen that before.
I first saw it in RadCom when it was first published.
I used his technique of mounting the 9850 into a 28 pin DIL header on the first one I used.
The same author wrote a series of articles describing various amateur radio applications using the 16C84. Yes it was that long ago, 20 years. Where does the time go when you are having fun?
Anyway, his key feature was squeezing the maximum out of the PIC by using a lot of multiplexed I/O.
I remember a comment by Blue Room Bill about PIC I/O multiplexing:
"If you need that much I/O, you need a bigger PIC"
An idea which I very much agree with.
I do not want to detract from the info in the application note, but if you were doing it again today, you would do quite a few things differently.
JimB