Depending on just how "ultra micro" you refer to, Mr. Newell might have a few good ideas, he has some awesome planes including an 8-channel 1:96 scale P-51 with retracts, and he is active on RC Groups too if you can't find some ideas from his YouTube channels.
His account on RC Groups:
Martin SJ
There are plenty of smaller micro-actuators and screw type servos available for the smaller size planes that would be helpful for this project I'm sure.
I'm still new, but I wanted to help here, and sorry if this wasn't the type of help you were hoping for but I thought the tiny P-51 with retracts was a good inspiration for you at least!