Will a Jeep Cherokee 4.0 exhaust header fit?

Will a Jeep 4.0 exhaust header fit my 72 Gremlin with a 258? 

On the 1972 head? Nada. But alot of people swap the 4.0 head to get the header to fit. Personally, I would put a 2 1/2 pipe right off the stock manifold and run that all the way back. I know there's going to be people telling you about backpressure and all that. But I've put big pipe on stock exhaust manifolds, and it was a decent gain, and reliable. I've done it enough times t
Now. And the important thing is to run a complete exhaust. Don't believe you'll burn valves. Trick is run a complete exhaust. When you drag race, why do engines run faster with open headers? Think about that. I'm going to tell you like it is. But it's your car.

I have two 4.0 headers laying around if you need pics or measurements.

You can MAKE a 4.0L header fit, but requires some work. The different levels isn't a big deal, because you will need to cut the flange off the 4.0L header and make a new one to fit he 258. The center tubes have to be bent slightly to touch then welded together. Any good welder can do it, not sure it's worth the cost though. You can get a used 4.0L head, header, and valve cover from a pick-n-pull yard for less than you can buy a new 258 header from Clifford and be way ahead of the performance game, even if the head needs rebuilding. Modding a 4.0L header would be a bit less than the Clifford, and probably as good -- especially if you split the flange and run a pair of 1.75" pipes. I'd run no larger than 2.25" single pipe on a street performace engine, but 2.5" won't be too big -- I just don't think there would be any gain (maybe at very high rpm) and the 2.25" should be easier to fit under the car.