I got one that is off a big twin, the difference is on the custom the bracket that comes off the bottom triple tree is wider at the point that the headlight bolts to it, mine is the same width. JP has the mount for $6 I saw. Or a simple block of metal if you are handy.
The ring on this one is like the non "custom" style, the bolt goes right to left rather than front to back.
Here is a stock picture of the light I got.
Wire is about 6-8" long and ends on a 4 pin black socket.