Cliford Simek worked at the paper where I am also employed. Fox B. Holden, Fox B. Quick: not much appears on the internet. El-Ron, of course, went on to other things in the science-fiction genre.
Cover by Mort Lawrence. Not a lot of info online, but at least he's remembered.
These were the kind of covers i liked to see in the second-hand shop - streamlined rockets! Mars! Men on strings!