Updating a C50-C60 1964-66 Long hood

[stsalvage]

Not to sound stupid witch it will be.But I'm looking to invest into 2 of these old chevy trucks from the 1964-66 trucks.I'm not looking to keep the factory engines in them.I want to Up date to modern LS or Duramax.What are the pit falls of running these types of engines in these old trucks.

I'm looking to run hydro boost brakes Run the newer power steering box AC and run the Allison 6-9 speed.

My question's are can i make the 1980 and up front Ibeam work in my older truck cus i want to run disc brakes.

Do i need to update the rear end for the automatic trans or can i just use the one that came with the truck.it will be check cleaned and fixed if needed.

Would it do any good to run a Air bag system under the truck for handling and comfort.Just asking Questions