you'll get best performance by using the stock internals with the addition of the 4.0L header/exhaust. i would also recommend using the 4.0L injection
you can take the complete stock 4.0 EFI system (including the ignition) and put it on your 258 using the 4.0 head. You'll have to do a little wiring work, and you'll need to get a harmonic balancer and crank position sensor kit to make it all work, but at least it all bolts together. Hesco is the place to go for the Harmonic balancer kit.
Another option is to just put the complete 4.0 in your Jeep. You'll need the same harmonic balancer and sensor becuase your current bellhousing won't have a provision for the 4.0's crank position sensor, but otherwise it's a bolt in.
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-James-
1988 YJ Laredo
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you can take the complete stock 4.0 EFI system (including the ignition) and put it on your 258 using the 4.0 head. You'll have to do a little wiring work, and you'll need to get a harmonic balancer and crank position sensor kit to make it all work, but at least it all bolts together. Hesco is the place to go for the Harmonic balancer kit.
Another option is to just put the complete 4.0 in your Jeep. You'll need the same harmonic balancer and sensor becuase your current bellhousing won't have a provision for the 4.0's crank position sensor, but otherwise it's a bolt in.
------------------
-James-
1988 YJ Laredo
[ ] | || || || [ ]