You should have no trouble replacing your current power system with a brushless motor and matching brushless ESC. If your radio system is not unique to your plane, the transition would be easier.

If you are referring to a brushed 380, which is about the same as a Speed 400, there are many, many motors that would be suitable. Very generally, look for 1 oz brushless outrunners rated at about 1000 - 1300 Kv. A motor of this weight can handle about 100 watts of input power (voltage x current) without overheating with very high efficiency. Swinging something like an 8x4 to 10x6 propeller, a motor in this class ought to provide enough thrust to power the plane you describe very well. A brushless ESC rated for 15-18 amps would handle a motor in this class comfortably. I would go with a 3s lipo rated from 800-1600ma.

You will probably have to shift the battery position forward a bit to get the right CG as the brushless motor and lipo are much lighter (assuming you are using Nimh). I highly recommend reading the many excellent stickies on this site dealing with power systems and motors. Also, google Hobby City and look at the range of motors, ESCs and lipos that are available for very reasonable prices. You will be amazed at the number of options available. Good luck with your conversion!