5.7 is fairly direct, though you will need to buy some adaptors etc. You will need electric fans, i got dodge intrepid ones. You can use the 4.3L computer and wire harness, but you will need the 5.7 harness also to mash together with the 4.3 harness for the fuel injection etc. The O2 sensors have to get changed to ones from an Express van and re pinned. You MUST use headers to install a 5.7 in the 4x4 s10, because of the steering shaft it will not clear 5.7 stock exhaust manifolds. I mounted mine on 2.8L engine mounts with 2.8-V8 adaptors from advance adaptors. The build thread is in the NOS section of the site for photos progress etc. I had someone with a lot of S10 v8 swap experience help with the project as far as parts procurement and installation. He did all of the install work for me while I was away at work training for 3 months.
To do a 5.3, or any LS motor swap in the S10 you will need a new computer, a special made wire harness and the LS motor itself. Its quite a bit more expensive to do and unfortunately was out of my budget at the time when I did my swap.
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Exploration Machine- 02' CC V8 swap. 300K+
Portable Roller Coaster- 07' MKV VW GTI
Its another Jeep- 98 TJ