In summary, the steps were:
* demodulate bell 202 tones (UZ7HO soundmodem)
* break up KISS frames
* identify relevant frames and strip AX.25 headers
* parse Winlink B2 blocks
* LZH decompression

The problem is worked with Python code as well as some VB.NET at the original writeup.

Original writeup (https://www.sohio.net/markdown.cgi/pbctf21/isthatyourpacket.md).