Oh man it's actually kinda fun! Tear down the block to bare block and send it out to be machined perfectly flat, get a 4.2 crank, find a matching cam or go lopey, do a full valve job, pistons and rods should be cleaned completely, and new rings installed, unless you have it bored out, then you need new pistons and rods, rings, and I'd suggest a 5 angle valve job. While its out, your going to need to update the transmission and such, advanced adapters plate with a good heavy transmission because the ax15 or the jeep automatic isn't rated for a 350 ft lb torque engine. This is not a job you want to half ass. You need new main bearings, new rod end bearings, fully floating pistons, etc etc etc

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ASE Certified Automotive Service Technician.

Well, I'd check out the flex plate and torque converter first, sounds alot like main bearing knock when the flex plate cracks. After that I'd measure the crank and see if you might need undersize bearings. The bearing clearance is supposed to be .002 inch. Depending on the condition of the rest of the engine you might be able to get away with reusing the existing pistons and such, but I'd still do new rod journal bearings.

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ASE Certified Automotive Service Technician.

As far as the transmission goes like I said, it's not rated for that high torque. I'd consider changing it out, or beefing up the one you have, or even getting a tranny from an older 4.2 or the 304 renegade. Still. It's not a direct fit but it's not as pricey as some I've seen.

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ASE Certified Automotive Service Technician.

http://jakesracingengines.nstemp.com/jeep%20page%202.htm. Yeah.. It's not a really economical way to do it but at least you can build a parts list :)

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ASE Certified Automotive Service Technician.