A note on various of the Gutenberg SF entries: the versions on Project Gutenberg may be the magazine serial versions. They may differ substantially from the book versions. (Shorter, to fit magazine space limitations.)
Copyright law was different back then, and magazine versions had different copyrights than book versions. In many cases, magazine copyrights were not renewed, but book copyrights were, so you'll see magazine serial versions on PG but the books won't be available.
This is particularly true for E. E. Smith's Lensman and Skylark of Space series: the book publication versions aren't on PG. (I have no idea who currently holds the rights to the Lensman series.)
It is possible to find them on the darknet, but quality will vary.
Copyright law was different back then, and magazine versions had different copyrights than book versions. In many cases, magazine copyrights were not renewed, but book copyrights were, so you'll see magazine serial versions on PG but the books won't be available.
This is particularly true for E. E. Smith's Lensman and Skylark of Space series: the book publication versions aren't on PG. (I have no idea who currently holds the rights to the Lensman series.)
It is possible to find them on the darknet, but quality will vary.