Single AA/14500 mini maglite (the Micro mag)

This shows how he did it:

It requires opening up the ID of the tail part and cutting down the OD of the threaded (head) part. Then gluing them together.
He talks about replacing the spring too. Maybe the switch linked above would mean you didn’t have to do that. You would just need to contact the seller to find out the current rating of the switch.
I prefer having tail switches on my MiniMags anyway.