Fender Mount Top Turn Signals

I have a 71 Scamp and it didnt come with the fender mounted turn signals, the holes where there just no signals. I picked up a pair of them at a junk yard and compared them to many others that were there. They all looked the same.

So I went to install them and I noticed that they do not cover the final hole in my fender. I have 3 holes. 1 large one for the socket, 1 small one for the screw and the 3rd ??? no idea??? So can anyone tell me how long your turn signals are on your Scamps. These measure up to be around 1.75".

Also Do you guys have 3 holes in your fenders also?