Water intake nipple corroded

I have this Slant 6 out of a 70 dart that I picked up from a guy to go into my 68 Valiant and it looks like they been running straight water in the motor for a long time. Everything is rusty!!!!
When I removed the top water return for the heater core, I noticed the nipple for the hose was falling apart at the very top. Should I attempt to replace it or just leave it alone and use it as it is? There is about a 1/4 inch missing on the top. I'm afraid that if I attempt to remove it, It will either crumble or break off short in the head and then how do I get it out?

I have a picture of the nipple I am referring to. It goes into the top of the head close to the water pump which is underneath it.