I hope I'm not too late here! Please don't buy a spare BA/10. The first few years I had my 89, I had the Peugeot so I know what I’m talking about here. I know you said you don't want to do any modifications but you really should take a second look at how much modification it actually takes. I have the 4.2 also and when I put a new NV3550 in, it was a lot less involved that I thought it was going to be and I did it in a weekend with a buddy. Advanced Adapters makes a kit specifically for the swap, and you'll be going from a light duty transmission to a medium duty one. The aforementioned is true for the AX15 as well, and will cost a little less.
For the swap to the 3550 here’s what had to be modified…
1) You have to open the t-case (which isn’t as scary as it sounds) and replace the input, which comes with the kit. /// I have an extra one of these in the garage if you’re interested in making a purchase ///
2) There’s a bracket that comes with the kit that moves the shift lever of the t-case back into position
3) The pilot bearing has to come out of the 4.2 crank and get replaced with a larger diameter brass one that comes with the kit.
4) There’s a specific bell housing that’s sold to mate the two, again with the kit.
5) Lastly, it changes it to an external slave from an internal for the clutch.
That’s it. Everything is bolt on. I would assume it's much the same for an AX15 swap.
