Cylinder head

The machine shop will check the heads for flatness. If they are not warped then you are good to go.

Pressure testing is not standard procedure so ask for it.

All good advice, take the cylinder head(s) to a machine shop and have them checked over. Better yet, buy rebuilt cylinder head(s). It might be wise to get a price estimate on checking you old parts at the machine shop versus rebuilt parts.

Any GOOD machine shop will at the very least, do a magna-flux test to check for any cracks in the heads, after a thorough cleaning, and check for any warpage at all. The heads should be stripped down(valves and guides removed)before cleaning. A magna flux test is probably not as good as a pressure test due to certain interior passages that they may not be able to view that could have cracks in them, and certain cracks will only open/close under hot & high pressure. Either way, as long as you have them off, you should have them cleaned, checked and machined/re-surfaced if needed and also have the valves and seats re-ground or lapped, new valve guide seals installed, then reinstalled with new gaskets. No sense doing 1/2 the job and possibly needing to do it all over again.

I am pretty sure you can not Magnaflux an aluminum cylinder head. The Magnaflux company makes dyes that can be used though.

3.0 engines had cast iron heads and 3.8 engines had aluminum cylinder heads. Not sure which engine the OP has.

You are right Bob, you can't magnaflux alluminum heads, which is exactly why I didn't specifically address the head materials.Since I didn't know which one his heads are made from, & that is also why I recommended pressure testing, because it wouldn't matter then.