Doh! I just realised that mine are the English edition of Penthouse. Bob Guccioni, the original founder of Penthouse, sold UK publishing rights to a UK publisher and they made up magazines that were targeted at a British readership, with appropriate advertising and editorial. The early English editions had some pictorial spreads by Guccioni and other US Penthouse photographers but they included some European photographers' work as well. By the mid '80s UK Penthouse had changed hands again and lost most of it's US contributors. I only have a few issues from 1983. I've had a look through them but unfortunately I can't find Greta Anderson. However, I'm sure you should be able to pick up the back issues of US Penthouse through eBay. Best of luck.