I'd say that there's no guarantee that a new neck will swap right into the pocket on your body, but your can measure your pocket and make sure that it's close. If your bass is a good clone of a J bass, I'd expect it to be a decent fit.
I got a franken-Jazz a few years ago that already had a P type Warmoth neck and I bought a new Warmoth J neck for it with my favorite size frets. Before it could go in, I needed to have it finished and the heel needed to be drilled to take the mounting screws - it didn't just come to me ready to drop right in, but if you found a 2nd hand neck, it might swap right in without needing any work. Again, no guarantee.
I also swapped a Modulus fretless into a J body, but that required the holes under the pocket in the body to be redrilled. The issue there was that the neck had threaded inserts for the mounting bolts to screw into, so there was no wiggle room. Both cases required minimal luthier intervention, but the necks were so much better than anything I've seen in knock-offs or even recent US Fenders that I've had absolutely no regrets. Warmoth necks are nicely stable, but they're certainly on the hefty side (steel rods instead of graphite for reinforcement) and graphite necks in general are just alive with sound, I suppose because there's no wood to absorb certain harmonics.