The only reason I suggested the P-device is the top of H is the "source" and the bottom is "sink". So you use P's on top an N's on the bottom. Im thinking of max volts/amps right now.
Wait a minute... Wonder if they used NPN for both! Usualy the setup is PNP on top and NPN on bottom!
Check around the PCB. They may be running a "switching inverter" PS for the receiver and decode IC. The chip set need at least 2.2 volts I think to run. If so there may be 3v running around that could be used.
PS: Good job!
