Some people might be interested in the Public Domain Super Heroes wiki.
I’ve been trying to find a similar listing for heroes from the ‘pulps’, but there doesn’t seem to be one.
None of the main characters in The Case of the Syphilitic Sister are pre-existing characters, but they’re intended to be recognisable ‘types’.
I thought they had added some of the pulp characters to the PDSH wiki.
They have a few, but they seem to be mostly characters that have also been in comics.