Also check out season 1 of https://malicious.life/. S1E02 specifically covers The Dark Avenger, but the whole of S1 was awesome (and he rest too. But S1 especially).
Maybe I'm confusing DAME with later mutation engines that had more elaborate ways of transforming the decryptor and payload code. I know there were some pretty sophisticated JIT-type things in the latter part of the DOS virus era.
But it sounds a bit more prosaic than OP made it out to be (maybe it's incomplete?)