Tattered and Lost Ephemera did some digging on Lowell Grant and post this:
"I have not found anything definitive about “claytoonist Lowell Grant,” but I have found information about a Los Angeles based sculptor named Lowell Grant, and it’s very sad. According to the site filmforno.com (here and here) , Lowell Grant lived in Echo Park. He did sculptures for the Vincent Price movie Diary of a Madman. He also did work that was in collections all over the country such as churches, libraries, banks, and public buildings. Alas, Lowell Grant died in the 1970s when the kiln in his home blew up killing him and burning down the house. Apparently all that is left is the foundation which can be seen here. The site was used in a movie called Mi Vida Loca.
This book has been on my shelf for decades and I never took the time to do any research. Now when I do I look for information it ends with a sad story. I can’t be positive that the man who did these book illustrations is the same man who died in the explosion and fire, but I think it’s plausible."
see more at http://tatteredandlostephemera.blogspot.com/2012/11/manners-and-claytoonist-lowell-grant.html