GNU poke: The extensible editor for structured binary data
I always liked Winhex for this type of thing.  It could dissect a structure with a c-like syntax.  I found it as shareware as a kid and have never used a hex editor I liked more.<p><a href="https://www.x-ways.net/winhex/" rel="nofollow">https://www.x-ways.net/winhex/</a>