Designed to fit on top of an extendable lamp arm with a 45mm diameter bolt, this allow 3 GU12 LED lamps to replace the old lamp head. Should work with all sorts of comparable lamp heads, I used this to replace an old strip light head with something more modern.

Print out three of the lamp holders, one lid and one of the two bodies. You might want to flip the lid to print it out the other way up.
Should require just a little cleaning then you should be able to push fit together. I found that the GU12 mounts I used were a tight fit into holders so I didn't glue those but I did glue the holders to the base.
I assembled all the wiring on the holder then attached to the head. On both the lights I have done the wiring comes through the middle of the bolt.
I used computer fan mount screws to attach the lid to the box (I have millions of these). If you don't have any you might want to consider making the mounting holes finer to suit whatever you have.