Turn signal pigtails for 1971 sharktooth grille

[RockinRobin]

So I bought a pair of pigtails for my 1971 sharktooth grille from Classic Industries part #3513307. Tried them on and they don't fit, they are too small to twist into the socket.
Apparently the pigtails for '71 and a '72 are different, and Classic doesn't make the ones for the '71. Any idea where I can find the right pigtails for this grille?

 

[RockinRobin]

UPDATE: I need to talk to someone who really knows these grilles, because the housing has an arrow and the word "LOCK" on the back which would make me think it uses the twist lock style, but it also has 2 small screw holes at 6 and 12 o'clock like the screw on type would use. I'm wondering if there is some intermediate piece of plastic that goes between the housing and the pigtail.