Yeah those are cool and one of the oldest packs i have. A lot of the 1977 ones have the Kenner logo on the back and i believe they're pre-toy release too judging by the ad on the back of this pack-
Here's the back of the series 3 pack. (yours is series 5)
taken me a while to get a photo of these but here is Chris' prize I won in the Xmas draw. 4 very nice loosie's that are top notch and look sweet in my loose collection.
Cool, might be a while as I have 3 more collectors series to build and check. Millenium Falcon, Super Star Destroyer and Death Star II. Will let you know when they are ready.