As has been pointed out and acknowledged, Warren Kremer created the Harvey comics house style that the other cartoonists followed. This makes it a bit hard to tell the different artists apart. All the main characters are basically the same design. Little Audrey is Casper with ears and clothes and hair. One way to tell the different artists apart is to look at the incidental characters in the stories. Each artist drew the non-regular characters more in their own styles.
Spooky is a generic Harvey character, but the ghost next to him is a very specific design.
Howie Posts's incidental characters are generally more specific and cartoony than the other cartoonists at Harvey.
They are also cuter; they have big heads in proportion to their bodies. Some of the Harvey artists draw really tiny heads and eyes - which isn't very cartoony.
This cover is likey by Warren Kremer. Good looking and well balanced.Here is a stark contrast between the Howie Post comic on the left and the other artist on the right. Bill White says it's Kremer, but then that makes me think someone else did the cover since that's in a different style.