^^^ That's excellent advice. To that, I can only add a few things from my fun times with the A4LD.
The exhaust Y-pipe won't be fun; hit all of the bolts well in advance with PB Blaster, Kriol, or even ATF. The only gasket you'll likely need is the one between the cat and the Y-pipe.
The block plate IS very important, and make sure that the hollow locator dowels at the 9 and 3 o'clock bolt positions are in place when the new mission goes in.
Check the flexplate very carefully for stress cracks around the crank bolt holes (common failure point).
As Ron said, if the engine rear main seal shows any sign of leakage, change it while you're doing the swap.
If your truck does not have an auxiliary ATF cooler, add one.
Good luck!