New heads install
 

Its fine to reuse, but best if you keep the same pushrods with the same rockers. Just inspect each one carefully.

It's ok to reuse if they are the same head and have not been cut. Aftermarket heads or other model # you'll have to measure and replace if necessary.

lube them up and install them,you will be fine.

Check geometry if you deck the heads or block. Also check geometry if you change to a different head, rocker, head gasket or valve stem length. Sometimes you need a different pushrod length. It's good practice and you won't have that issue to worry about.
Most don't need a change, but if you miss something it can get ugly.