This is the same response I gave you in the Pm. posted here for the benefit of others.
With a wiring diagram a multi meter and a 12 volt test light. the factory harness could be trimmed of any unnecessary wiring, and used to run the new power plant.
to give you a better idea of what is needed to be done, I would need to know more about the project and what your vision of the completed project would be.
For example I would need to know exactly what options your car has,
Like do you have power windows, power door locks? Factory alarm system,
do you have A/C, etc
Pretty much how hard this will be depends on what you expect from your car.
wiring of the old 350 is easy and can be done using the factory harness, and a few relays.
This will be time consuming yet inexpensive, you will need to purchase some items.
To rip out the current harness and install a generic Harness from Painless wiring means you will have to reinvent the entire car, this will be time consuming and cost more yet the end result will be much cleaner.
If your serious about the project,
Tell me more about the car you have and all the options, skip nothing regardless of how minor it may seem.
Tell me more about the motor and transmission you want to use. tell me about the motor and transmission that is currently in the car you own.
I will say if you have a great running 350 motor and transmission with gobs of power. and the V6 firebird is currently running and reasonably good looking.
This conversion will do nothing but make it worth even less than it is.
You would be doing this for your enjoyment only.
A Chevy 350 and turbo 350 dropped in a car like this one that I am drooling over would make more since because the work you would be doing and the parts you would be adding are meant to be in a car like this and would significantly increase this cars value. well beyond what your parts and labor investment would be. provided you have a good running reliable engine purchased at the right price.
I have a complete 4 bolt main 69 350 with a turbo 350 with every part needed to complete this project and I only have 800 bucks in it. this would make this moderately price project worth doing. buying and or building a new engine and all the accessories would make less sense. for resale purposes.
http://miami.craigslist.org/pbc/cto/5422954003.html