I gave it a try and it got me a smidge closer. I ended up trying a bunch of different scriptable hex editors like Hexinator
(ended up being my favorite so far, but still lacking in scriptability), and WinHex
...
Then I noticed someone had replied and their answer accepted on your StackOverflow post linked. They included a link to the documentation for the specification.
In the end I decided I would get what I want fastest by just writing a script to dump the binary without expecting any of the classes to be in scope. So I wrote it in Node.JS.
Figured I'd share here for you or anyone else interested in doing something similar:
https://github.com/mikesmullin/csharp-assembly-dump
Cheers! And thanks for the inspiration. ๐