Leonaur published virtually all the Edgar Rice Burroughs novels
in what was the closest we've come to seeing a matched set.
Unfortunately, they did this without obtaining permission 
from Edgar Rice Burroughs, Inc. of Tarzana, California.
ERB Collector/Researcher Laurence Dunn has shared these 
Leonaur cover images in our ERB Online Bibliography Series

Leonaur Press is a UK publisher of historical fiction/biography, 
but they also feature Fantasy and SF titles. 
Their focus is on early authors and they reprint editions long forgotten. 
These are good books, simple, the sets are very appealing,
but getting some of them is next to impossible now
- its not even a question of price, they just aren't available on the market.