Blocks don't usually warp, but an overheated head very well could. If the head is new you won't need to worry about it. If it's used and being rebuilt then it will be checked for flatness and milled if it's not flat.

Head gaskets are not made to seal a warped block or head, they are ment to seal two perfectly flat surfaces together. That's why torque and sequence is so important when installing a new head.

 

alright so if i do do a rebuild its more dependent on how long the head has been on the old block to whether or not ill have to mill the head i get ya

 

Maybe a better way to say this is, if the machine shop has any professional experience with rebuilding a head they will check it for flatness and mill it if necessary. Decking the head is not that big a deal. It only cost about $150 for a complete head job.