Carbing a 4.0L HO head is more common than you'd imagine.
The biggest obsticle in mating the old intake on the new head is usually needing to find some larger diameter heavy washers or horns to fill the gap between the old intake and the required 4.0 style exhaust manifold.
The newer aluminum 4.2 intakes are better breathing but I've had no reports as to sucess of mating one of these over the older cast iron versions.
In either case, I might suggest holding a 4.0 intake gasket over the 4.2 intake and see if you could do a little 'match porting' - especially around the head's injector bump up.
Tip: According to Bennie at HESCO, Permatex "Ultra Copper" gasket sealer is about the best if you care to use anything on the gaskets.
Note: It is said that any silicone based compound is hell on the O2 sensor so ... "a little dab will do ya" ... use only a very thin coat if you use anything.
Tip: Fel-Pro exhaust gaskets are about the best out there. Each port hole has a metal squeeze ring and using a compound is unnessesary.
Tip: CJDave always endorses using studs and double nuts instead of regular manifold bolts.
JAF
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