* Different engine blocks and heads: The 32-valve engine has a completely different cylinder head design and likely a different block casting. The 16-valve head simply won't bolt onto the 32-valve block.
* Different intake and exhaust manifolds: These are unique to each engine design and won't be interchangeable.
* Different computer systems and wiring harnesses: The engine control modules (ECMs) are entirely different and incompatible. The wiring harnesses are also unique to each engine, requiring significant modifications or a complete harness swap.
* Different accessories: The placement and mounting points for accessories like the alternator, power steering pump, and A/C compressor are likely different.
* Transmission compatibility: While both may be mated to similar transmissions, the bellhousing may not be compatible, requiring significant adapter work.
Even if you could somehow overcome the mechanical differences, the vast differences in the engine management systems would make it nearly impossible to get the 16-valve engine to run correctly in the Navigator. The effort and expense involved in making such a swap would far outweigh the potential benefits, if any. It's simply not a feasible or practical swap. You'd be better off sourcing a used 32-valve 5.4L engine for a more straightforward repair or replacement.
