To all of the above replies!
Most likely you will have blown cooling seals to start with.
How come you overheated?
Low on coolant or just racing your motor for a long time?
Check your cooling system for bubbles and if you see any milky-ness or foam u got blown cooling jacket seals.
Since your rebuilding it shouldn't be a problem if your motoris still running but you might hav to replace a front or center iron. The seat fo the cooling seals are very thin in some areas causing them to crack and become unusable.