Yes they can warp. I've read that they can even crack when re-installing.
First check both manifolds with a straightedge. If warped, best to have a surface grind.
I had mine off to work on a stuck heat riser.
Make sure everything is clean on the mating surfaces.
It's a balancing act getting the intake, alignment rings and exhaust loosely bolted in.
I do finger tight. Tighten from the center out.
Sometimes I have to lightly shake the manifolds to get it all centered up.
If an alignment ring is not in place properly, you can crack the manifold.
Then maybe a half turn on each bolt with the wrench and repeat till it just becomes snug.
Final tightening is torqued to 15 to 20 ft/lbs (check the shop manual for the spec).
The problem is that the access area is limited to most socket type torque wrenches.
I practice hand tightening on an accessible bolt and check with a torque wrench till I get the feel.
Mine leaked with new gaskets.
I let the exhaust cool a bit, put on some gloves, then loosened the exhaust bolts a little and then re-torque.
