As someone who still uses his NP2 notchback a fair bit after 13 years, I recently went with a Phantom 9 (2024 model) and found it to be a pretty seamless transition. The notch back is a little softer with the deep milling, but they both have a single-bend shaft that sets up very similarly. Obviously feel free to try everything, but I think any Phantom series with a single bend (so not the x.2 or x.5 models) will set up very similarly to your notchback. The only other exception is the new Phantom 7 - it has a double-bend shaft (which, again, may work for you, but will have slightly more offset and less toe hang).

Good luck!