Indeed, the Cobra 1500 uses the Antares fin sheet.

as posted here on YORF :

http://plans.rocketshoppe.com/estes..._Cobra-1500.pdf

Note the part # for the fin is BF-76 ( as in 1276, Antares ) .

many of the reused fin sets can be ID'd this way , as they use the part # of the eariest release, although easier to acertain on early kits with 1200,1300,etc part #s instead of the modern #s as quoted.

~ AL