the stock engine harness only needs power added at a few locations to operate , i used one for a 70 chevy pickup and basically spliced into the wires at the driverside , theres three fusable links in the harness , use 1 for power in to fuse box and ign switch , used a switched source coming from the vehicle to relays hotwired off the other fusable link power feeds to run the inj/coilpack ,and the pump
only other thing you need is to connect the starter relay and lamp for the generator to charge (goes to gen idiot lamp ), inside the car the ecm gets connected
the other connector by ecm thats for the dash only needs a 12v switched source , ground , the ground signal from a brake switch if you want lockup and has output for scanmaster
caspers electronics should be able to do hybrid harness as a standalone. if youdecide to go fast classic i have a casper standalone harness that i was going to use in my 69 firebird that i may part with