Putting 2.9L A4LD behind 4.0L bad idea?

[Tibbits]

Would It be worth putting one that came off a 2.9L 4X4 onto my 4.0L? I found one on craigslist for a few hundred bucks. My mechanic says he wouldnt waste 1200$ on a new A4LD because my 4.0L engine could blow at any time, they suposedly have head problems and mine leaks a tiny bit of coolant into the #1 cylinder.

 

[Bent Bolt]

The 4.0 version is built a bit stronger than the 2.9 version. It will work but for how long ?????