I am going through this right now because I am getting rid of my ba10.
I picked up an AX15 with an NP231 out of a '93 YJ up in Minn.
It turns out it has a 21 spline input shaft.
I got some replies here on JF and traded shafts with one member but it won't go into my planetary gears???? It appears the od of the shaft, not including the teeth on the outside is more than what my old 21 shaft was???
I also got another shaft with the pg's but it is about 1/2 longer and that shaft will fit my pg's but don't know if there will be a problem using it with the longer length.
You should be able to swap yours out if they are both 231's I am not familiar with the 207.
Here is some youtube on the reassembly
There are 4 of them and they are very detailed. I believe there is a disassembly vid too.
I don't think one is stronger than the other but the 23 spline is the newer and more common setup you will find.
And welcome to JF and Jeeps! You will get your questions answered here, I am new to jeeps too and it has been a great help, even if it empties my wallet.