pyagid no, 4.2 was carb and 4.0 is Fuel injected. You could put a 4.0 head on a 4.2 block with some slight modifications, make a stroker motor out of it http://www.monsterslayer.com/jeep/40Head/40Head.htm -Paul
pyagid if you look at that link it explains them all. Basically you need to fill the waterjackets in 1 side of the head
