I just got a headlight bucket and socket with the adjusting screw above the connector. I was looking at it and realized the terminals were vertical in the socket so if you turn that socket 90 deg's you can use most headlight bulbs that can be gotten today. The later headlights have the terminals in the vertical position with the adjusting slot is on the side instead of on top. If you install the early style socket in the later style headlight it moves the terminals to the horizontal position which matches the contacts on most modern bulbs putting the filaments in the horizontal position rather then incorrectly in the vertical position.
With a little work you can install an NH throttle shaft in a Kingston carb. (at least an L4)
The 1915 and 1916 headlight bucket has the focus screw at the top. Look at the bottom where it attached onto the fender bracket, the shoulders are square instead of tapered.
The double contact for those lights need to be vertically aligned because the right angle connector needs to point down. Today's reproduction sockets are perpendicular to the focus screw.
: ^ )
The vendors sell a correct reproduction of the right angle plug with vertical contacts for 1915-16 lights.
As Keith says, they also sell a right angle plug with the horizontal contacts for use with later headlights.
HOWEVER - at least on Lang's website, the photos for the sockets are swapped -
It's debatable if the angle plugs were used in the 1917 Model year. For 1917, the adjustment screw was still in the 12 o'clock position. However, the '17 Rip Van Winkle touring and my dad's '17 touring came with straight plugs. Royce Peterson's '17 roadster has angle plugs but his father may have swapped out the originals 60 years ago - I'll have to ask him. I have an unrestored '17 roadster but the plugs were missing on the lights when I purchased the car.
I am suggesting using the socket from the early style head lamp in the later head lights. You would just use the straight plug.