1950's-60's Pinup Painting by Hagan

Eye-popping 1950's-60's pinup girl, fresh from a Chicago area estate. Signed HAGAN, an artist who left little or no evidence of a career, which is leading me to believe that this is the pseudonym of another artist. This painting is so good, spectacular in person, and it is clearly the work of a top-notch artist, that I believe this was done as a side job by someone more famous, and under contact to another publisher. Interestingly enough, this came from the estate of a former employee of the Inland Litho Co., a large Chicago printing company, back in the day. He probably picked it up when it was being thrown out.
Right now, this looks like the work of Al Buell to me, who is known to have painted under his "Al Leslie" pseudonym. The script signature is also in the Buell style, although this does have a certain 1960's Elvgren look, as well. It also looks similar to the work of William Medcalf.
(I have managaed to flatten out the crease since the photo was taken).
Any ideas?