Got the bars and computers in the mail today. Avenir takes a pretty standard button battery that needs replacing, Cateye MITY 8 battery is still working.

I pulled the technium from the stack and swapped the drop bars for the flats, I found a pair of old short-pull levers lying around (might look on ebay for some smaller ones). My son now has a lot easier time braking. In a few years I will be able to put the drop bars and road levers back on. Just need to get some grips, might even put the bullhorns on, if he wants!

Pics before & after: