These were offered as accessories several years before Henry started installing electric lighting as standard equipment.
Here's five sets I have gathered over the years and haven't gotten around to restoring.
The late Max Edmonds showed me how to remove the ears from a damaged fork mount bucket, cut off the flange and use it as a Templete to scribe the cutout for the ear onto a single stem bucket less the stem.
Fill the old single stem mounting holes, cutout the openings for the fork mount brackets, and rivet them in and take it from there.
Max made and sold quite a few sets of these that he made from trashed fork mount lamps that he saved the fork mount brackets from.
1911 Motor Supply Co. catalog: