Well, after extensive googling and typing in keyword after keyword, I found the answer to who illustrated the x-rated movie posters signed "Weston." This most excellent artist was a man named "Armand Weston." Oddly enough, the trivia page on IMDB for "Heat Wave" lists him as the artist:
IMDB: Heat Wave
Also, I found the following link:
Men's Pulp Mags
Weston, as the pulp mags author writes, truly was a multi-talented guy. Illustration artist and both director and producer of XXX movies? What a combo!
Also, I've seen the movie "Defiance of the Good" (which he directed), and it was good, sleazy fun.
Now, if I could just figure out who illustrated "A Teenage Pajama Party", my life would be complete...
And to those of you who lost out on that lollipop, better luck next time!