I know someone that had me make a set of JP's for one of those pp's just like yours when they first came out. he was happy with his shaft at the time, but Alot of meucci players use a predator on theirs that I know of. The thread size should be 5/16x18, and is actually one of the most common sizes. Depending on the type of insert used, Most makers & some repair guys should be able to handle It with no major problems. There are quite a few people on AZ that can do It, Like Ted here mentioning He could, or even a local guy if setup for that sort of thing. If you want to save your ring work, then I suggest getting someone very experienced & well setup for It, because not much room to true things up after reinstalling the old ringwork, without having to build the finish up thick to match the butt. It needs to be centered perfectly with the insert & shaft blank for best results IMO.
Just me, but If It were me, I would keep the old shaft original, and just get the closest match I could for the predator ring work. Seems like an mp ivory material may match the material in that cue, but without seeing the 2 side by side could not be for sure, and the brown ring could probably be bored and cut from a piece of Coco.
Good Luck with it.
G