I just checked the part numbers for the two I have; one with and without the "Magnum" and thunderbolt. The part numbers are the same 2484679 for both.
There is another eBay listing for the identical Magnum version with a different part number as well 2483671?! Listed as being for a 66.
http://www.ebay.com/ulk/itm/331714928274
Maybe the plain version is also a magnum version and the "Magnum" and Thunderbolts added in the later years with a different part numer(?); Just a guess.