here are a few wiring links i used when doing my lt1 swap.
http://www.lt1swap.com/lt1_pcm_pinout.htm
http://www.lt1swap.com/95impalalt1.htm
its pretty easy to turn the factory harness into something like the painless one in just a few hours. i'd save the $700 for something else. and like muddyjimmy said above, research,research and more research and if you don't have a donor car, find one! be on the lookout for a ex-cop car, they have the biggest/best cooling system, quick ratio steering pump, gas tank/fuel pump and the lifetime silicon "garden" hoses.

