Chevy Vortec 4.3L in jeep cherokee 1985

Ok I want to drop a 3.4L into my 85 cherokee to get rid of the gutless 2.8L. And I have heard lots about the 3.4 and how simple it just might be. But what are the pros and cons between the 3.4 and 4.3. like cost, gas milage, modifacation and preformance?
 
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