Cool, I think the tray will work well for you. I haven't really thought much about the tail motor, as it is the tail works pretty good with the stocker. Many of the modded mcpx's that have gone bl are running the 120 tail motor. I do have a 5 amp esc laying around, maybe I'll see if I can scavenge a motor from a cd rom.
As it is the 120 is flying ok but I am having problems with the low end of the power curve, if I want to lower the altitude most of the time the motor stops and I have to gun it to stay in the air. It's like an on off switch. I've ordered this 2s motor http://www.hobbyhot.com/SWANGHOBBY-3...ess-Motor.html
, should be here this weekend. It has a 2mm shaft so it will be much easier to try different pinions and ratios.