These are the same transfers as were used for Shell Vintage Cars, so check out that page to see them. They're waterslide, made by Decal Transfers (NZ) Ltd., & not Letraset-related, but as you may have noticed, I like to include the odd item that's interesting, although strictly speaking off-topic.
They were originally marked "An exclusive special from your Shell Dealer", but evidently that is no longer the case. I haven't so far been able to pin down a date for either promotion.
Original photos courtesy of chocolatefrog
Picture Credit: The SPLAT Scan Archives — chocolatefrog
© Tom Vinelott 2020