My MIA P bass was once black also. I wanted it white. I had someone else refinish it (a car painting place) but did all the stripping and primer myself.
I used generous amounts of Lacquer thinner to get the finish off followed by a ton of hand sanding. There's probably better, less toxic, chemicals you can use to help but that poly finish is tough as nails and lacquer thinner seemed to be the ticket at the time
I had no problems with just unbolting the neck and laying it down in the case while I did this.