Unfortunately, Horizon/E-flite/Parkzone doesn't publish specifications for their motors. But it looks to be roughly the same shape/size as a Power 10. So you might get lucky, and find the Power 10 will fit in the plastic mount included with your Trojan. If that's not the case, you'll have to figure out how to mate the Power 10's x-mount with the plastic mount. You've got a similar problem if you use the Turnigy motor: it looks like it's shorter than the E-flite motors, so you'll need to deal with standoffs and making sure you get the CG right on the plane. As for the ESC, the Turnigy is supposed to be a 22/28Amp motor, which the 30 amp ESC in the Trojan should handle. HK spec's it for a 40A ESC; mu guess is either the Turnigy or the Power 10 will function fine with the existing speed control.

On the Apprentice, I'd plug the G25 into the existing speed control and see if it works. The good news is that ESC's are coming down in price. I'd just take it easy on the throttle, and it'll probably work fine.