I have to do more research, but I remember seeing activation of gear doors by using string. You tie the string across the doors and as the gear comes up it pulls the string up and closes the door. The gear open the doors by pushing the doors open when extending. I believe I saw this installation on the Combat Models F-16. I'll have to pull the instruction video and manual to see if there is more detail. Hopefully someone on the new, Construction of the VQ P-61 forum, will have ideas also. Anything more I find out will be posted there.