Impact or Hand on 11 Year old RUSTY Exhaust nuts !!

So whats everybodies opinion. Gonna have to remove to manifolds. After the normal Kroil soak, what do you all suggest to try to avoid broken studs in aluminum head. I have a stubby impact that I can get into most of them or should I tackle by hand

Definitely remove the manifold to head nuts by hand. Try to keep the ratchet perfectly perpendicular to the fasteners. Save the impact for the other end at the flange bolts.

Use heat if you can get it in there without crisping something.
Heat the nut up with a propane torch, then use rust penetrant to cool it down. The hot fastener will wick the oil deeper into the threads. Spray it til it stops smoking, then wrench it out. This method also works fantastic for the manifold flange nuts and bolts in combination with your impact.

The flange nuts and studs are the ones that snap most in my experience. The ones in head generally come out, but I never go for the impact right away. If the first couple come out without a fight using a ratchet or wrench, I'll grab an air tool.
I just swapped an engine into a 29 year old Mitsubishi Eclipse and had no problem using my air ratchet to remove the exhaust manifold. And trust me, there's plenty of rust in Massachusetts

Like Rev Scott suggested, heat is your friend, and quenching the hot fastener in penetrant usually works very well.

If I'm being extra cautious, I'll start by trying to cracking the fastener clock wise a hair before trying to remove it. Once you've got it moving if you meet resistance, run it back in a couple threads and work it in and out in small increments.

Hope not being too late to the party....

Use an induction heater and you'll be fine! Impact is a no go!