Price out a replacement truck *double gulp*
If i wasn't able to do what your planning to do myself i would be looking for a shop to do it.
Have you checked out what it would cast to have the work done by experts in the duramax ?
It may cost a bit more, but the peace of mind knowing that your truck will be good for another 18+ years motor wise anyway.
I would compare a price from Kennedy to what you have so far with their experience in mind.The final product may be worth the extra cost.