A 700 watt motor is less than about 1HP.

While that plane will fly in a very scale like manner with a .32-.40 glow engine ( in the same wattage range ) I would opt for at least an 800 watt or greater motor.

There is plenty of room to cram a PAIR of 3000mAh 14.8v LiPo packs in there or a single 5000mAh 14.8v pack... but it will be progressively harder to get over the 700 watt range with a single 14.8v pack. You may want to opt for a 6S setup instead using a motor in the 550kv range.

You have to remember that motor specs are OPTIMISTIC assessments of motor performance and if a motor is rated at 700 watts you'll probably see something more in the 600-650 range at best.

You can purchase a suitable motor mount, and the ESC will fit in the nose/cowl for best cooling.

However your biggest problem will be the lack of an access area to swap out the batteries while at the airfield.

There is no area on the bottom of the plane that would accept creating an access hatch.

From the top it MAY be doable, but you would have to be very careful.

You would also half to re-inforce the carbane area as you will be effectively weakening the area used to re-inforce the carbane and firewall.