A purchased module. I just had to put the headers on. This one is adjustable so it's important actually to adjust it using the little pot. ;)
Originally I'd put two single headers, but then when I decided to use the 90degree ones, I further decided to use 4 headers connected for added strength, which means trimming down the pins that have no corresponding holes on the module.
In retrospect if I had mounted the female header further to the left and reversed it's direction, and then soldered the DC-DC board's headers "backwards" under it, it would have fit better on the board without an overhang. Next time.
The 9V battery clip's leads are thin and fragile and I've already broken one at the solder joint. Some type of adhesive or strain relief would be good.