Jonathan,
You've got a lot of work ahead of you!
Here are some more suggestions and replies to some of your answers/questions above.
2. I don't remember the brands, but Diesel Power magazine has talked about all of the different aftermarket Duramax wiring harnesses at some time or another, finding one that suits you needs is a critical part of this convrsion. You could also get some input and advice on that and your entire project at
www.4BTSwaps.com.4. I wouldn't use rear disc brakes unless you already have front disc brakes, or swap to disc front and back at the same time.
For the booster, ditch the vacuum booster and use a hydrobooster, they work off the PS pump pressure, are smaller, and much better/more powerful. Lost of info and advice can be found here, as well as parts if needed.
http://hydratechbraking.com/hydroboost_faq_old/6. Do you already have the axles you want, or will you be swapping some? Just curious, I don't have any advice here other than try to make the tires fit under the fenders if possible.
This calculator may be helpful for calculating what gears you need
http://www.onlineconversion.com/bigger_tires.htmTire size makes a significant difference, so pick that, pick how fast you want to drive, know your OD ratio in the transmission, decide what RPM the engine gets good mileage (I'm not sure for the Duramax, but guessing 1,800 or so?), then calculate what axle ratio you need to get you there.
Sounds like fun,
Grigg
