still trying to finish up my 4.9 swap. I put my exhaust on, started it up and noticed white smoke/steam coming out of the right dual. I shut it down, waited for it to cool off and checked the water level. Sure enough it was low. How common is it for the 4.9 to have a cracked head and or a blown head gasket? Or could it possibly be something else? Thanks for the info & advise, without you guys this swap wouldn't have been possible.

Did you remove the Heads or Intake Manifold during your build? IF so you might not had tightened the bolts in the right order to the right spec''s. With Iron Head/Aluminum Block motors it is rare to get a cracked head, the block will develop issues before the heads will in my experience. It is most likely a head gasket issue.

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Buy or rent a coolant system pressure testor. Pressurize the system and look to see where it is seeping from

Dump the oil and see if there is coolant in it. If it is leaking it will be at either the top of the sleeve (gasket) or the bottom (o-ring) - either way the motor will have to come apart.

It may be better to just get another block as the gaskets cost more than you can usually pick up another motor for. That being said, buy only the GM gaskets for the oil pan and intake and make sure you get a good quality head gasket (make sure it has the metal rings) and o-ring - speaking from experience...

I did not take heads or intake off prior to installation, put motor in complete. There isn't ant coolant getting into the crankcase. Started it back up this morning, put my hands over the exhaust tips and my right hand got wet, left hand stayed dry. can someone refresh my memory on how to magnaflux a head its been 20+ years since i did my last one?

Do a compression leakdown test and that will confirm what is wrong ,like mentioned above head gasket or O ring is the achilles heel on these motor also these heads never crackat all get another motor it is cheaper than repairing the motor.