Fixing heater core hose pipe on Intake manifold

I had my Heater core hose pipe break off clean at the top of the intake manifold last night. I have a plan for fixing it, but thought I'd run it by the experts first.

I want to tap the hole with a 3/8ths "Pipe Tap" (a regular tap won't work)
Then thread a 3/8ths galvanized 3" nipple with a union threaded to the othe side. The union should get me to roughly the inside Diameter of the hose coming from the return side of the heater core.

Main thing I see is that the 3/8ths pipe is quite a bit smaller than the plastic piece that was fused on originally, but it beats the plug that I have in there now

Let me know what you think.

Just wanted to let you all know, I took my car into Ford to get this fixed and they covered it in the extended warranty issue that is discussed in the sticky.