I've done some gasket replacements on the older 350 but haven't done one on one this new. They much of a bitch?

Not a big deal at all. Just look up the torque down specs. Pretty strait forward job on a 350.

Goodluck!

Ls1? You'll need some copper rtv. Wait until it cures a bit before you put the manifold back on. You want it to be slightly tacky.
Retorque the bolts again a few days after driving as well.

As far as taking the manifold off, it's easy. Just make sure you make note of where the parts came off, etc. I use a shoe box to label the location of each bolt I take out of the manifold.