Hi, I did the same thing to my S-10 a few years back. What year/engine was your S-10 originally, and what are you running (electrically) on the V8? If it's just a carb and an alternator, should be pretty easy.
If you haven't got any wiring diagrams, try your public library. If they have an Alldata or Mitchell's subcription, you can print out what is needed.
Are we Talking a Straight Swap here? Or an older engine (non~Computer) in a Computer Controlled Vehicle?
The Basics are:
The Main battery Cable and Fusible link (the one that goes to the fuse block) To the big bolt on the starter.
The Brown wire to the "S" Terminal on the solenoid.(from "Start" on the Key)
The "I" Side is used for secondary Ignition (power during start cycles)Coil
HEI 12 volts From the "On side of the key switch.
The alternator, Internal or external regulated ?
1 or 3 wire?
1 wire goes straight back to the Starter solenoid Main Bolt terminal or the Battery...3 wire goes through the system to power the light ,Field ,and main power, The External regulator will require a slightly different hook up...
The Senders are another thing, you will have to identify the individual sender wires and hook them to the engine in the proper sequence...
Tell me more about the swap, maybe I can help you more.