Assuming you have the hardware (engine/trans/misc), there are a couple companies, like www.pacificp.com (PPE) and www.bankspower.com (Banks) that produce custom wiring harness and computer packages that make it simpler, but their kits are relatively expensive.

Try to locate a bundled "package", that contains the hardware/electrical you need. Occasionally, you can find a salvage dealer or someone who lost interest who are offering package deals. But, for those who can find them, a salvage truck saves them both time and money. While we tend to look at the engine/trans as the big buys, all of the little things add up to about the same cost. Little things would include items like wiring harnesses (~$600 each, need 2-3), computers/modules (4-5 of them for a complete system), complete steering column, radiator (~$700), intercooler (~$700), intercooler hoses/pipes/clamps (~$600), lower radiator hose ($~150), and on and on.... you get the point - ask me how I know what these things cost... I got a screaming deal on the engine/trans, but the little things really ran the cost up.

People have gotten the engine to run on their shop floor without being in a vehicle, just by connecting the harnesses/computers/fuel/batteries. So, just do the same thing with it bolted into your chassis. Other than vehicle lighting, plan on swapping in the complete Duramax wiring system. Once you make that leap of stripping-out the original FJ75 wiring system, the project actually gets easier.

Jim