I have an issue with my 2001 XJ. When I bought the Jeep it had a blown-up engine and the automatic transmission was cooked. I transplanted a 4.0L and an NV3550 from a 2001 TJ into my Cherokee. The engine lasted about three years but is getting really tired. After two blown head gaskets I am ready to replace it. How do I mate the good 5.2L V-8 I have from a Grand Cherokee to the NV3550 I am using in my XJ? Can I find a stock bellhousing to do the job, or does anyone make an aftermarket bellhousing or an adapter? One more question. Do you know if the 5.2 is internally or externally balanced? I will thank you now for any info you can send my way.
Not being intimately familiar with the swap you propose, I turned to the experts at Advance Adapters (advanceadapters.com). Unfortunately, the news is not good for your exact swap. As you've already figured out, the 4.0L and the 5.2L Mopar engines do not share a bellhousing bolt pattern. The NV3550 was used behind 4.0L Jeep engines exclusively, but a close cousin to the transmission, the NV3500, was used behind the 5.2L (318ci) V-8 in select Dodge Dakota and Ram 1500 applications. Unfortunately for you, even though they are close to each other, not much interchanges between the NV3500 and the NV3550 that you already have in your possession. According to Advance Adapters, even though the NV3550 has a bolt-on bellhousing, the NV3500 does not, therefore it cannot be swapped for one that came stock behind a Dodge truck with the 5.2L. Further, Advance does not offer an adapter to mate the 5.2L to the NV3550, and I was not able to find an aftermarket adapter that would make your swap viable.
However, all is not lost. Dodge Dakota and Ram 1500 4x4s with 5.2L V-8s and NV3500 transmissions share the common six-bolt pattern and 23-spline output shafts that mate to the NP231 that you likely already have in your Cherokee. If you can source a Mopar V-8 NV3500 from a Dakota or Ram 1500, then it will bolt to both your V-8 donor engine and the transfer case that you already have. The NV3500 and NV3550 are also dimensionally similar, so it should fit into place. Finding a Mopar NV3500 may be difficult since V-8 manual options were a bit unusual, but they are out there. These transmissions were used behind 1994-2001 Ram 1500s and 1994-2004 Dodge Dakotas.
Even though you have the Mopar V-8, you may want to rethink your swap. Cherokee engine compartments are tight and were never designed for a V-8. You will run into a lot of packaging issues with your swap in addition to the transmission challenges. There's also wiring, exhaust, and other challenges. And at the end of the day you won't pick up a whole lot of power and torque over the 4.0L you already have. The 4.0L I-6 is a great engine. You may want to think about either rebuilding the engine you have or sourcing a good used engine. Local Craigslist prices run anywhere from $450 to $650 for a good used 4.0L, and I believe that’s pretty consistent across the country.
It's also possible that your existing 4.0L has a warped head, which is not all that uncommon. Assuming the bottom end is good, you might try swapping the head or having the existing head resurfaced and rebuilt.
Lastly, Edelbrock (edelbrock.com) recently came out with a trick aluminum head that has gotten great reviews. Though a bit pricey, even an Edelbrock head may be a cheaper upgrade in the long run.