4.0 head on 4.2 conversion

I did the conversion myself. There are a few good links to how to's you can find on Google. Bill Hughes has a link I'm sure. I got the head from a rebuilder who only wanted an inline six head in return as a core. So I gave him my 258 head and I didn't lose for that. I also got a header for $150 that, while its not a boorla, it works fine. Lastly I had to have a custom headpipe made to fit between the header and the muffler. Duotone in PB took care of that for about $50. The difference was incredible. I gained a ton of power and gas mileage also improved. I used JB weld and packing peanuts for the coolant passages and after 18 months everything is running fine. The jeep has seen daily driving and even a cross country trip last October. Would I do it again, absolutely. My only difficulty I had was with rods. Just be careful with the pushrods. I had guys tell me I can use the 4.0 rods and others said no I should use 258 rods. I had to have a custom set made. Fortunately, I was living in San Diego at the time and Crower cams took excellent care of me. If you want to know how to measure for them I can help you there.