1992 np231 question

So I am swapping to a 231 mainly for the HD sye options they have and more than likely 4.1 in the near future. My one concern is my spline input on my 242. I found a great deal on a 231 with AA HD sye and tera 2 low, I understand many xjs that have a 242 have some oddball input shafts, the 231 is a 23 spline input(im 90% sure) and i dont know what my 242 is. So my question is if I dont have compatible input can I swap out the input shaft on the 231 for one that matches mine? Also what spline inputs are the 241OR cases? for about 650 more than the 231 I can grab one of these from a buddys rubi with 6k on it. Really kind of torn but dont know if the 4.1 will really help me out at the moment.

IIRC all NP242's are 21 spline.