Go for it!
I'll second the 3/4 or 1 ton idea.
A good engine and /or Allison will be expensive.
It would help if you are mechanically inclined and a good fabricator, or have money.
Subscribe to the magazine called "Diesel Power" from Primedia. It's a great mag, and just this month they had several articles about diesel swaps, and a few months ago they had some Duramax swaps. You will learn a lot from it about what needs to be done for the swap, and what can be done for more power. Write a letter about your ideas, they should have some good answers and suggestions.
Grigg
