Yea, my son and I had that same thought when he decided to install a 5.9 with the electronic trans into his 57 Dodge wagon. He bought a running motor, trans, factory wiring harness and computer.

I've rewired several cars in my time, and I have adapted a coupe of efi throttle body systems to older cars, wiring in not new to me.

That said, I spent many hours between the factory wiring diagrams and the actual wiring harness trying to determine what I could eliminate (not using the dash or overhead monitoring consul), and trying to reduce the process to one fuse box. In the end, I came to the determination that if it would work, it would be great, but if a problem devolved, I would have no way of knowing what I may, or may not have done wrong.

My son finally bought the Hot Wire Kit. We had 4 wires to connect to make the motor run, it came with a fuse box, and there were feeds built into the harness to power several options. Best of all, there is a real person on the tech line, if you have a question or an issue. We had one we created ourselves, and they helped walk us through fixing our mistake. We should have done that from the start, it would have moved the car building process forward by several months.

I guess you need to determine what things you "farm out" on your project, and what you do yourself. A custom engine harness on a computer controlled motor and trans is a pretty complex part of a large project that many would be overwhelmed by. I can wire the car, give me a free standing functioning engine harness, which Hot Wire has done. Gene