Sharktooth grille park/turn lamp pigtail issue

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? The hole for the pigtail is perfectly round and has a small screw hole at the 6 and 12 o'clock positions but an arrow with the word "LOCK" over the top of it. Is there a piece that goes in between the two?