Take a look at the metal Thunderhawk that GW put out in the mid-late 90s. You'll see that it's basically the same as the picture.
When the Blood Angels Codex first came out there was a ton of speculation on the BA boards about what the Stormraven looked like and wether or not there were any pictures to be had. This, along with a dozen others, was considered and rather quickly discarded. All of them are Thunderhawks. Some look odd due to artistic interpretation and others due to crappy perspective skills on the part of the artist. But they are Thunderhawks.
"As a rule of thumb, the designers do not hide "easter eggs" in the rules. If clever reading is required to unlock some sort of hidden option, then it is most likely just a result of wishful thinking." Pete Haines
For the Emperor's sake people it's a TURRET! There is no such thing as a turrent.