I've been doing LOTS of research on this very subject for an upcoming project (either a Kelly or King V, whichever I find the best deals on). What I've found is this: most Jackson necks will fit into most Jackson neck pockets. However, you have to consider scale length of the original instrument. A 22-fret Dinky neck may fit into Soloist body, but if that Soloist body originally had a 24-fret neck and had its bridge routed for a 25.5" scale length (for example), it may be impossible to intonate and tune properly because the Dinky neck will be shorter than what the Soloist body was configured for.
That being said, I'm positive that if you find a Jackson neck with the same amount of frets and scale length, it should fit into just about any other Jackson body.
Does that make sense? I literally learned all of this in the last week or so, so anyone with more knowledge please chime in.
Also, this thread is a good reference for the problem you may face if you install the wrong neck:
BTW, if your neck has the 3x3 headstock, 24 frets, and a locking tremolo nut...let's talk, maybe we can make a deal.