Road rage dont put your hopes down so fast, fortunately for you shinysideups statement was incorrect.

Both the 390 and 360 are FE motors, I really am not certain if all FE motor heads are interchangeable but my guess is that they are. Hope that brought your spirits back up after shinysideup smashed them into the ground! im jp. I'll look into it and make sure they are interchangeable for you.

EDIT: Ok yes good news 360/390 heads can be changed! They are the same motor with different strokes 360=3.5... 390=3.78